Fixes #35: Profile foss-parent-verification not activated properly for Maven-Plugins.

Currently the profile foss-parent-verification is set to be activeByDefault (see pom).
However, when another profile is activated (e.g. foss-parent-run-its for running invoker tests because src/it exists), foss-parent-verification is not active anymore (see Maven's introduction-to-profiles). Another example would be during release, where the maven-release-plugin will set performRelease=true, this will inactivate foss-parent-verification as well.
Solution: Activate the profile, when src/main/java exists, the checks are useful only when there are sources anyway.