Fix test case with wrong parameter in test_quota_classes

The 'id' parameter is filled in the quota-classes request body in
unit test, but it is not necessary. 'id' is passed to the server
by the URL but not the body. This patch fixes this bug.

Change-Id: I4014264e16031382277f6f1b520556a2a2690ad8
Closes-Bug: #1266634
Merge "Fix test case with wrong parameter in test_quota_classes"