This commit updates the Maven plugin to generate a
`META-INF/boot/build.properties` file with various build-specific
settings (group, artifact, name, version and build time). Additionally,
the plugin can be configured to write an arbitrary number of additional
properties.

A new `BuildProperties` bean is automatically exposed when such a file is
present. If that bean is present, an `InfoContributor` is automatically
created to expose that information under the `build` key.

As for the git contributor, it is possible to only display the core
settings or everything using the `management.info.build.mode` property.

See gh-2559

Rather than exposing a raw String with the epoch time, GitProperties
now exposes the actual `java.util.Date`. `InfoProperties` has been
improved to return such data type when the raw value is an epoch time.

* pr/5384:
  Polish

Closes gh-5384

Closes gh-5129

Closes gh-5343

This commit polish the new info contributor infrastructure by migrating
`GitInfo` to `GitProperties`. `InfoProperties` provides an abstraction
that exposes unstructured data in an immutable way.

The `GitInfoContributor` now accepts a "mode" that determines if all data
should be exposed or only a sub-set of known keys.

Closes gh-2644

Previously, if SpringApplication.run failed due to the refresh of the
application context throwing an exception, the application context
would not be available during run failure handling. This meant that
null was passed to any SpringApplicationRunListeners, however the
javadoc for the finished method does not indicate that it is possible
for null to be passed in. In addition to the possibility of a
NullPointerException, a side-effect of this behaviour was that the
auto-configuration report was not produced when refresh fails, making
it useless as a tool for diagnosing refresh failures.

This commit updates SpringApplication to take a reference to the
application context as early as possible and, crucially, before it
has been refreshed. This means that refresh no longer has to succeed for
the context to be passed to any SpringApplicationRunListeners and that
they will now receive an inactive context, rather than a null context in
the event of a refresh failure.

Closes gh-5325

Previously, the Launcher would call ex.printStackTrace for any
exception that was thrown when launching the application. This was
unnecessary as the stack trace should already have been logged by
the application when it failed to start.

This commit removes the call to ex.printStackTrace, thereby allowing
an exception to be logged only once or not at all after successful
failure analysis.

Closes gh-5358

When the bean validation API is on the class path, but there is no
provider available, the stack trace that results is pretty much
useless. All the user needs to know is that the have the Bean
Validation API on the class path and that they should also add
an implementation, such as Hibernate Validator, if they want to
use validation.

This commit introduces a FailureAnalyser for ValidationException,
that returns a FailureAnalysis when the ValidationException is a
result of the situation described above.

Closes gh-5332

Due to `@ConditionalOnClass` and `@ConditionalOnMissingClass`, the
behaviour of many auto-configuration classes is dependant on the
contents of the class path, yet we do not have a lightweight way of
testing such classes against a specific class path.

This commit introduces FilteredClassPathRunner, a JUnit Runner that
runs a class’s tests using a filtered class path. A
`@ClassPathExclusions` annotation on a test class can be used to
filter entries from the project’s default class path, thereby allowing
a configuration class’s behaviour in the presence or absence of
certain classes to be tested more easily.

Closes gh-5359

Add a `@JsonComponent` annotation that can be used to indicate that a
Bean is a JsonSerializer and/or JsonDeserializer that should be
registered with Jackson.

Support is provide via a new `JsonComponentModule` which is
auto-configured in `JacksonAutoConfiguration`.

Also add `JsonObjectSerializer` and `JsonObjectDeserializer` classes
which provided as a convenient base for serializers that work with
Objects.

Fixes gh-3898

Following the changes made in ff99bb07, Tomcat’s WebAppClassLoader is
set as the thread context class loader of the main thread. If Tomcat
was stopped while the main thread was still running (typically as a 
result of a startup failure), this had the unwanted side-effect of
causing Tomcat to report that the application had started a thread named
main and had failed to stop it.

This commit updates TomcatEmbeddedServletContainer so that, during stop
processing, the current thread’s context class loader is reset before
Tomcat is stopped. This prevents Tomcat from incorrectly believe that
the application has started and failed to stop the main thread.

Closes gh-5357

Closes gh-5335

See gh-5335

Prevent the validation support to kick in if the Validation API is not
available.

Closes gh-5353

Support for Velocity has been deprecated in Spring Framework 4.3 with
the plan being to remove it in 5.0. This commit deprecates Spring
Boot's support in 1.4, with the plan being to remove it in 2.0.

Closes gh-5276

Previously, if Couchbase was available on the classpath but not
configured, Spring Boot would attempt to scan the project for
repositories anyway.

This commit makes sure that it only happens if an infrastructure
bean required is present. The tests have also been rewritten to better
reflect what would happen in practice.

Closes gh-5349

In certain environments, such as Jetty configured with centralized
logging, Spring Boot's logging system can be problematic.

This commit adds support for using the existing LoggingSystem system
property, configured with a value of none, to disable the logging
system and rely on the standard logging configuration mechanism for
whatever logging framework is in use.

Closes gh-3571

* gh-5310:
  Upgrade to Gson 2.6.2

Closes gh-5310

* pr/5345:
  Polish

Closes gh-5345

Previously, the ehcache statistics were computed on the activity of the
last minute which gives a "live" overview. All others cache managers,
including JCache, provides a "cumulative" metrics (i.e. the hit/miss
ratio since the creation of the cache or the last time it got cleared).

Ths commit aligns the ehcache statistics to provide a similar semantics
as the other cache managers. The side effect is that the metrics are now
available, even if there is no cache activity at all at the moment.

Closes gh-4891

Assert using epoch time

Add TimeZone in date assertion

This commit updates `GitInfo` to use a proper `java.util.Date` rather
than a raw String. Because the Maven and Gradle plugin do not agree on a
format, `ProjectInfoAutoConfiguration` now registers a `Converter` that
is taking care of translating the raw `String` to a `Date`.

See gh-2484

This commit updates "simple" configuration classes to use constructor
injection. Simple means that there are no optional dependencies
(@Autowired(required=false) is not used), and none of the dependencies
use generics.

Configuration classes that are not simple will be updated in a second
pass once https://jira.spring.io/browse/SPR-14015 has been fixed.

See gh-5306

* pr/5328:
  Polish contribution
  Rename HealthIndicatorAutoConfigurationProperties

Closes gh-5328

Closes gh-5326

* pr/5303:
  Polish contribution
  Add Cache Properties for RabbitMQ

Closes gh-5303

Closes gh-3502