glusterd: Simplify glusterd_service_stop()

Change-Id: I396d250a3299ad1f7fce4bd14389b0c2756b6cb0
BUG: 764890
Signed-off-by: Krishnan Parthasarathi <kparthas@redhat.com>
Reviewed-on: http://review.gluster.org/4718
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Anand Avati <avati@redhat.com>