Add some tests for volume quota set and get rid of TODO about
using the value instead of the key to get the attribute.
Change-Id: I57aa57951aeea65965966e63af922cda532d759d
When using the command: openstack quota set, the compute quota below
can't be set successfully,the value of compute quota stay unchanged,
'fixed-ips', 'floating-ips', 'injected-files', 'key-pairs'.
What's more,I add a TODO comment in the code for two reason.
1. volume quota set works fine for the moment.
2. To indicate that this issue about volume needs
discuss and report another bug, if it's confirmed.
This bug is only about compute quota.
Change-Id: Ic1028d561f5a0030cf65ac18fc117bf01e945478
Partial-Bug: #1420104
