glusterd/snapshot : Dont acquire a lock if config is of
type DISPLAY.

Problem : Currently we are acquiring a lock if we give
"gluster snapshot config <volname>". As this is just a
Read-Only command, we need not acquire a lock.

Solution : This patch checks if the command given is of
type DISPLAY. If so, then glusterd_v3_mgmt framework is
not called, as reading information from local node is
enough.

This Patch also fixes "Assertion failed: volname" while
doing the system config change when snap create was in
progress.

Change-Id: Ie8991f2cd746987b11152006e113e8706516138b
BUG: 1087677
Signed-off-by: Sachin Pandit <spandit@redhat.com>
Reviewed-on: http://review.gluster.org/7458
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Vijaikumar Mallikarjuna <vmallika@redhat.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>