+++ This bug was initially created as a clone of Bug #1111148 +++

Description of problem:
=======================

When we try to delete a non-existing snap, it should gracefully fail with error "does not exist". Currently it is failing as:

[root@inception ~]# gluster snapshot delete snap1
Deleting snap will erase all the information about the snap. Do you still want to continue? (y/n) y
snapshot delete: failed: snap snap1 might not be in an usable state.
Snapshot command failed
[root@inception ~]# 


This is a regression bug, it used to gracefully fail. The message "might not be in an usable state" only makes sense when a delete is started for an existing snap and for some reason delete fails to delete a snap and we print this message that "it might not be in an usable state", because we really dont know how much the back end clean-up has happened 

But, if we attempt to delete a snap which doesnt exist it should fail as:

[root@inception ~]# gluster snapshot delete snap1
Deleting snap will erase all the information about the snap. Do you still want to continue? (y/n) y
snapshot delete: failed: snap snap1 does not exist.
Snapshot command failed
[root@inception ~]# 


Version-Release number of selected component (if applicable):
=============================================================
glusterfs-3.6.0.19-1.el6rhs.x86_64


How reproducible:
=================
1/1


Steps to Reproduce:
===================
1. gluster snapshot delete <non-existing-snap>

Actual results:
===============


[root@inception ~]# gluster snapshot delete snap1
Deleting snap will erase all the information about the snap. Do you still want to continue? (y/n) y
snapshot delete: failed: snap snap1 might not be in an usable state.
Snapshot command failed
[root@inception ~]# 

Expected results:
==================

[root@inception ~]# gluster snapshot delete snap1
Deleting snap will erase all the information about the snap. Do you still want to continue? (y/n) y
snapshot delete: failed: snap snap1 does not exist.
Snapshot command failed
[root@inception ~]#

--- Additional comment from  on 2014-06-20 07:18:38 EDT ---

Version : glusterfs 3.6.0.20 built on Jun 19 2014
=======

While snapshots creation in progress on a volume , if snapshot delete is executed, instead of failing with "Another Transaction is in progress" it fails with "<snap_name> might not be in an usable state

for i in {1..100}; do gluster snap create snap_1_$i vol0 ; done 
snapshot create: success: Snap snap_1_1 created successfully
snapshot create: success: Snap snap_1_2 created successfully
snapshot create: success: Snap snap_1_3 created successfully
snapshot create: success: Snap snap_1_4 created successfully
snapshot create: success: Snap snap_1_5 created successfully


gluster snapshot delete snap_1_2
Deleting snap will erase all the information about the snap. Do you still want to continue? (y/n) y
snapshot delete: failed: snap snap_1_2 might not be in an usable state.
Snapshot command failed

------------Part of the Log-----------------------

 E [glusterd-locks.c:228:glusterd_acquire_multiple_locks_per_entity] 0-management: Failed to acquire lock for vol vol0 on behalf of 1edef405-58c2-4a81-b7a3-50925c6f8035. Reversing this transaction
[2014-06-20 10:57:04.097204] E [glusterd-locks.c:387:glusterd_mgmt_v3_lock_entity] 0-management: Failed to acquire all vol locks
[2014-06-20 10:57:04.097226] E [glusterd-locks.c:464:glusterd_multiple_mgmt_v3_lock] 0-management: Unable to lock all vol
[2014-06-20 10:57:04.097241] E [glusterd-mgmt.c:401:glusterd_mgmt_v3_initiate_lockdown] 0-management: Failed to acquire mgmt_v3 locks on localhost
[2014-06-20 10:57:04.097258] E [glusterd-mgmt.c:1821:glusterd_mgmt_v3_initiate_snap_phases] 0-management: mgmt_v3 lockdown failed.
[2014-06-20 10:57:04.097464] E [glusterd-mgmt.c:1311:glusterd_mgmt_v3_post_validate] (-->/usr/lib64/glusterfs/3.6.0.20/xlator/mgmt/glusterd.so(glusterd_handle_snapshot_fn+0x5fb) [0x7f8a0dde440b] (-->/usr/lib64/glusterfs/3.6.0.20/xlator/mgmt/glusterd.so(glusterd_handle_snapshot_remove+0x258) [0x7f8a0ddd7e88] (-->/usr/lib64/glusterfs/3.6.0.20/xlator/mgmt/glusterd.so(glusterd_mgmt_v3_initiate_snap_phases+0x152) [0x7f8a0ddebc32]))) 0-management: invalid argument: req_dict
[2014-06-20 10:57:04.097487] E [glusterd-mgmt.c:1944:glusterd_mgmt_v3_initiate_snap_phases] 0-management: Post Validation Failed