glusterd/snapshot: Move read-only xlator to client graph

read-only xlator is moved from server graph to client graph
so that AFR & DHT healing can take place at server

Change-Id: I140ec962330c59d3b44f9bc8084a1544a1fd6c54
BUG: 1061685
Signed-off-by: Rajesh Joseph <rjoseph@redhat.com>
Reviewed-on: http://review.gluster.org/7582
Reviewed-by: Pranith Kumar Karampuri <pkarampu@redhat.com>
Reviewed-by: Sachin Pandit <spandit@redhat.com>
Reviewed-by: Krishnan Parthasarathi <kparthas@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>