Adjust GitAPITestCase for JGit and CliGit differences in isBareRepo

The adjustments are not final, and are not readily explained, since
the core JGit implementation is being used in the JGit case and the
CliGit implementation is being used there.

Needs more investigation
Simplify JGit.isBareRepository implementation

Did not change automated test results.  Still different results from
CliGitAPIImpl.