Add quota commands

* Add quota set and quota show commands; these work on both
  the compute and volume APIs
* Add the --class variation on the above commands

Note: this replaces the existing volume-only quota commands and eliminates quota list

Blueprint: cinder-client
Bug: 1172064

Change-Id: I766d40e410e48f05e36e17e567a4f01a9411b40e
Merge "Add quota commands"