Test for trackingSubmodules requires >=1.8.2

Make sure that we have the required version level for tracking submodules.
Only add --remote if git is >= 1.8.2

git submodule update --remote will only work for versions of git >= 1.8.2.
So, force check it here.  If it's not the version expected, then we won't
be able to do the update properly and the using project will have to update
the SHA-1 in it's .git/config for this module to get the latest changes.  So,
basically, if not 1.8.2, default back to original behaviour.
Merge branch 'master-tracking-submodules' into master-work

Conflicts:
	src/main/java/org/jenkinsci/plugins/gitclient/CliGitAPIImpl.java
	src/test/java/org/jenkinsci/plugins/gitclient/GitAPITestCase.java