Add refs/heads/ prefix for git publisher

Add refs/heads/ prefix for git publisher

ERROR: Failed to push branch csit-verified-master-2016-06-15 to origin
hudson.plugins.git.GitException: Command "git -c core.askpass=true push
 ssh://rotterdam-jobbuilder@gerrit.fd.io:29418/csit HEAD:csit-verified-master-2016-06-15" returned status code 1:
stdout:
stderr: error: unable to push to unqualified destination: csit-verified-master-2016-06-15
The destination refspec neither matches an existing ref on the remote nor
begins with refs/, and we are unable to guess a prefix based on the source ref.

Change-Id: I98a3b0bb77ce9e845f63f9e32d8e8bf1f63832a6
Signed-off-by: Miroslav Miklus <mmiklus@cisco.com>