springboot Explicitly set java home in Maven Plugin integration tests

Hi,

I'm regularly switching between JDKs at the moment and noticed that RunIntegrationTests fails if IDEA is setup with JDK 13+ while the actual Java home (e.g. inside the terminal) is set to something lower.

This PR sets the Java home explicitly on the InvocationRequest in MavenBuild, so the Java version for the maven invocation matches the one that actually runs the test.

Cheers, Christoph

Comment From: wilkinsona

Thanks very much once again, @dreis2211!