Add tests of GitPublisher honoring env values

Attempting to duplicate [JENKINS-24786] from an automated test.  Does not
duplicate the bug.  Shows that GitPublisher honors some environment
variables.
If the user does not have overall Item/CONFIGURE on Jenkins but has Item/CONFIGURE on the specific project, then let them check the credentials
[SECURITY-158] GitSCMSource needed to be checked as well.

Amends 39d585a41d6a7b91d3a48b1344d4085297641b89.
[maven-release-plugin] prepare release git-2.2.7
[maven-release-plugin] prepare for next development iteration
Merge remote-tracking branch 'upstream/2.2.x' into 2.2.x-exploring-GitPublisher