Description of problem:
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While creating snapshot, the output message is not same when the snapshot creation is successful and when it fails 

Create snapshot with the snap name that already exists.
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gluster snapshot create snapa vol0
snapshot create: failed: Snap snapa already exists
Snapshot command failed


Create another snapshot 
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gluster snapshot create snapb vol0
snapshot create: snapb: snap created successfully

In the first scenario, we mention snapshot create:failed Snap <snap-name> exists
In the second scnario, we mention snapshot create: snapb: snap created successfully


The output message is not the same . We should get the same message in both the scenarios as shown below (as in the gluster volume command). 
This would be needed in automation when parsing is done 

gluster snapshot create snapa vol0
snapshot create: snapa: failed: Snap snapa already exists
Snapshot command failed

gluster snapshot create snapb vol0
snapshot create: snapb: success: Snap snapb created successfully


gluster volume command 
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Gluster volume create command:
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gluster volume create vol4 replica 2 10.70.43.74:/brick4/b4 10.70.43.151:/brick4/b4 10.70.43.32:/brick4/b4 10.70.43.71:/brick4/b4
volume create: vol4: success: please start the volume to access data


gluster volume create vol0 replica 2 10.70.43.74:/brick0/b0 10.70.43.151:/brick0/b0 10.70.43.32:/brick0/b0 10.70.43.71:/brick0/b0
volume create: vol0: failed: Volume vol0 already exists




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