glusterd : Made volume clear-locks use synctask framework.

Change-Id: Ia1fe3d0500d999c1f95b43c9e53947834e39d680
BUG: 852147
Signed-off-by: Avra Sengupta <asengupt@redhat.com>
Reviewed-on: http://review.gluster.org/4490
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Anand Avati <avati@redhat.com>