Update quota-class-set/quota-set throw 500 error

The server doesn't check whether the parameter "quota_class_set" 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: I431a836bd35f846790497d6179515e8d559e2cd0
Closes-Bug: #1249222
Merge "Update quota-class-set/quota-set throw 500 error"