The Maven POM does all the dependency resolutions for the
spring-boot-antlib project. Delegating this task to Ivy, which is
buried deep in the Antrun/Antunit part of the build, makes any kind
of proxy configuration much more complex.
The ivysettings.xml already has the local M2 repository configured,
but because the folder "repository" is missing, the artifacts, already
downloaded by Maven cannot be resolved from this location.
The Spring and Maven Central repositories should be removed from the
ivysettings.xml files in order to force all resolves to be done through
the local M2 repository. The POM of joda-time version 2.8.1 has an
optional dependency to joda-convert 1.2, which lets the Ivy resolve
process fail, because this version of the joda-convert library was
not resolved by any of the Maven POMs. It seems as if Ivy does not
respect the optional scope, defined in the joda-time POM.

Pass proxy settings to the forked process to make the Gradle distribution download work

Create a gradle.properties file for each Gradle integration test and writes the forking
process' proxy settings as systemProp.http(s).Host/Port to the properties file.
This configures the external process with the right proxy settings to let it download
the Gradle distribution via the HTTP proxy server.

Added a hint for Windows users to get the core.autocrlf setting right

When the core.autocrlf setting under Windows is set to false for example
All files are not converted regarding their EOL characters to the
Windows format with CRLF at a line's end. There is a checkstyle
validation that checks that all files have the system's line endings
and in some test-cases the value from the system property "line.ending"
is used to check test output. So without the conversion, those checks
are going to fail, resulting in build errors.

Fixes gh-4367, fixes gh-3816