cluster/afr: Eliminate locking in sh domain in metadata self-heal

        Backport of: http://review.gluster.org/9240

Change-Id: I2ab2ad9a02d88c299cfb32e0cf6baa44d1c2ee12
BUG: 1171077
Signed-off-by: Krutika Dhananjay <kdhananj@redhat.com>
Reviewed-on: http://review.gluster.org/9246
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Pranith Kumar Karampuri <pkarampu@redhat.com>
Reviewed-by: Raghavendra Bhat <raghavendra@redhat.com>
Tested-by: Raghavendra Bhat <raghavendra@redhat.com>