glusterd : Made volume-set use synctask framework.

Change-Id: I1aa08ca843b87839180f9097bca370270a856e6d
BUG: 852147
Signed-off-by: Avra Sengupta <asengupt@redhat.com>
Reviewed-on: http://review.gluster.org/4488
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Anand Avati <avati@redhat.com>