glusterd: Made volume-stop use synctask framework.

Change-Id: I88270f70538bb89d828bb51830b54e9f59be258a
BUG: 852147
Signed-off-by: Avra Sengupta <asengupt@redhat.com>
Reviewed-on: http://review.gluster.org/4491
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Anand Avati <avati@redhat.com>