Only hide gitdir if the repository isn't bare

This problem was raised on the jgit list
https://dev.eclipse.org/mhonarc/lists/jgit-dev/msg02675.html

Change-Id: I8ce8a159120ce3747d31d6f012c6d2c0d0ce7917
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>
Merge "Only hide gitdir if the repository isn't bare" into stable-3.5