Actions on updating volume quota class:
[1] Add cmd option 'backups, backup-gigabytes, per-volume-gigabytes'
[2] Add test cases for cmd quota-class-show and quota-class-update
[3] Fix according test cases
Now, cmd option '--consistencygroups' is not yet supported for updating
quota class.
Change-Id: I482ae501f15a103b9e07f4f17d182c853035dca9