We cannot use the "--short" switch since it only got introduced with git
1.7.10, which is not installed by default on popular Linux distributions
like Ubuntu 12.04.1 LTS.

Therefore stripping the "refs/heads/" prefix manually.

Change-Id: I3fb8e07e90e2ee8fdaa50836c1e982b47219e790
Reviewed-by: Orgad Shaneh <orgads@gmail.com>