glusterd/snapshot: Proper err msg for snapshot create command.

problem: Snapshot command fails if one or more bricks are not thinly
provisioned. But the error message is a generic error message which
is confusing to the user.

fix: Provide correct error message in case of failure.

Change-Id: Iad247f966423a8f73ef6da57cab7ed6cddc05861
BUG: 1145086
Signed-off-by: Rajesh Joseph <rjoseph@redhat.com>
Reviewed-on: http://review.gluster.org/8377
Reviewed-by: Krishnan Parthasarathi <kparthas@redhat.com>
Tested-by: Krishnan Parthasarathi <kparthas@redhat.com>
Signed-off-by: Sachin Pandit <spandit@redhat.com>
Reviewed-on: http://review.gluster.org/8800
Reviewed-by: Vijaikumar Mallikarjuna <vmallika@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
glusterd: Error msg for snapshot status for no existing snaps should be aligned with error messages of info and list.

When a snapshot operation like status, info, list
performed on a non-existing snapshot.
For Status error message is displayed as 'Snap not found'
For List and Info error message is displayed as 'Snapshot does not exist'
Have the consistant error message all the places

Change-Id: I7b241217dba62fda844481731a6858e4ecb12897
BUG: 1145087
Signed-off-by: Vijaikumar M <vmallika@redhat.com>
Reviewed-on: http://review.gluster.org/8309
Reviewed-by: Krishnan Parthasarathi <kparthas@redhat.com>
Tested-by: Krishnan Parthasarathi <kparthas@redhat.com>
Signed-off-by: Sachin Pandit <spandit@redhat.com>
Reviewed-on: http://review.gluster.org/8801
Tested-by: Gluster Build System <jenkins@build.gluster.com>