list availability zones for compute

Adds the command `os availability zone list`

Change-Id: I77bf52a9b84a62c3771a4838c9ea0c3af03eedb2
Closes-Bug: #1400795
Catch exception when getting quota

Quota show command will list both the quotas of nova and cinder.
But if cinder service is not enabled, EndpointNotFound exception
will be raised and thus the command is broken. Catch this exception
so quotas of nova can be listed.

Change-Id: If2d2820675aa6a12e407d608fed846b21c953b2d
Closes-Bug: #1390507
Merge "list availability zones for compute"
Merge "Catch exception when getting quota"