Add valid check and unit tests on quota class

1.Cinder quota class hard_limit’s value should larger than -1 (-1 is a flag
value for unlimited).
2.Add unit tests for quota class.

Closes-bug: #1245360

Change-Id: Ie483db1bdbd4fac875de26abab8ebebd96f4938b
Create snapshot throws 500 Internal Error

The server doesn't check whether the parameter "volume_id" is in request body.
So the 500 error has been thrown.

We should catch the KeyError and transfer the KeyError to 400(HTTPBadRequest)
instead of 500.

Change-Id: I8a1dde1fd6ed820b39995af434efacc2a27c9604
Closes-Bug: #1252179
Merge "Create snapshot throws 500 Internal Error"
Merge "Add valid check and unit tests on quota class"