Closes gh-2723

Tomcat uses the strings “on” and “off” to enable and disable
compression. YAML interprets on as true and off as false, leaving
ServerProperties.Tomcat.compression configured with “true” and “false”
respectively. One solution is to use “on” rather than on and “off”
rather than off in the YAML file but users may not realise that they
need to do so.

This commit updates the connector customiser that configures compression
to map “true” to “on” and “false” to “off”.

Closes gh-2737

When configured with a context path of "", Undertow 1.1.3 changes the
context path to be "/". The change [1] was made to fix UNDERTOW-350
[2].

[1] https://github.com/undertow-io/undertow/commit/3db7707b8b34095d8d2fafecf94a10d101c62320
[2] https://issues.jboss.org/browse/UNDERTOW-350

See gh-2732

Closes gh-2670

Closes gh-2732

Closes gh-2730

Closes gh-2731

Conflicts:
	spring-boot-dependencies/pom.xml

gh-2735

Closes gh-2733

Closes gh-2729

Closes gh-2734

Conflicts:
	spring-boot-dependencies/pom.xml

Closes gh-2726

See gh-2718

Closes gh-2718

Previously, the ErrorPageFilter was not invoked for async dispatches.
This meant that an error that was set during an async dispatch would
go undetected and a 200 response with an empty body would be returned.

This commit updates ErrorPageFilter to configure its
OncePerRequestFilter so that async dispatches are filtered and the
correct error handling is performed.

Closes gh-2711

Remove unwanted System.out.println call

Closes gh-2702

Update SpringApplicationContextLoader so that the MockServletContext
uses FileSystemResourceLoader. This allows `/src/main/webapp` folder
to be found.

See gh-2654

Previously, SpringBootWebSecurityConfiguration required a web
application and @EnableWebSecurity to be on the classpath.
@EnableWebSecurity is in spring-security-config so this could lead
to the configuration being active when spring-security-web isn't
on the classpath but the rest of Spring Security is.

This commit updates SpringBootWebSecurityConfiguration to also make it
conditional on a class in spring-security-web.

Fixes gh-2717

Add an additional constructor to ServletRegistrationBean that indicates
if a URL mapping is always required. If set to false, the registration
will not longer use the default '/*' mapping.

Fixes gh-2596

Fixes gh-2598

Update SystemPublicMetrics to silently ignore ManagementFactory
NoClassDefFoundErrors which can occur when deploying to Google App
Engine.

Fixes gh-2701

* vcap-service-numbers:
  Support VcapApplicationListener Number Credentials

Update VcapApplicationListener to support Number based credentials.
Previously, any service credential value that wasn't a String would
be discarded. This was particularly a problem for services that exposed
a port as a JSON Number.  This change takes numbers in the credential
payload into account, converting them to Strings so that they will pass
through the properties system properly. There's no real downside to this
as Spring will coerce them back into Numbers if needed by an application.

Fixes gh-2707

See gh-2702

* gh-2698:
  fix typo in javadoc

{@code tomat-embedded.jar} --> {@code tomcat-embedded.jar}

Add note about escaping Spring property placeholders when using Gradle
automatic expansion.

Closes gh-2695

See gh-2630

Previously, the response from /health was not cached if the request
was secure, i.e. the user has authenticated, or the endpoint was
configured as not being sensitive. 

The commit updates HealthMvcEndpoint to apply the caching logic
all the time. Users that do not want caching can disable it by 
configuring the TTL with a value of zero.

Closes gh-2630

Previously, only a handful of properties could be set when
auto-configuring an Elasticsearch client. This commit introduces support
for configuring arbitrary properties using the
spring.data.elasticsearch.properties prefix. For example,
client.transport.sniff can be configured using
spring.data.elasticsearch.properties.client.transport.sniff.

Closes gh-1838