glusterd: Made volume-heal use synctask framework.

Change-Id: Ic6659335f18a3befcf9b8b3ca067883a2c889d03
BUG: 852147
Signed-off-by: Avra Sengupta <asengupt@redhat.com>
Reviewed-on: http://review.gluster.org/4493
Reviewed-by: Kaushal M <kaushal@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Anand Avati <avati@redhat.com>