added function to rename a git branch
added function to rename a git branch


Former-commit-id: ae852fb993265f55c917afaad01213b5727bddb9
subutai-io/Subutai,subutai-io/base,subutai-io/base,subutai-io/base,subutai-io/Subutai,subutai-io/Subutai,subutai-io/Subutai,subutai-io/Subutai,subutai-io/base,subutai-io/Subutai