Remove wait_for_image_resp_code

The nova api first creates an entry in glance,
before responding to snapshot creation request, so the entry
expected to be visible without any additional wait.

This change also introduces an OK code checker on the rest_client side,
it's extended usage can make unnecessary to assert the ok codes in the
test codes.

So the wait_for_image_status will implicitly validate the status code.

Change-Id: I9fdc1cc68501220e6688e2d7a745195b56d60cb9
Enable the quota test cases

The https://review.openstack.org/#/c/25887/ has been merged, we need
enable the quota related test cases.

Change-Id: I5187a109f0bacb1f3afa4276b3d73f47fd53ad87
Merge "Remove wait_for_image_resp_code"
Merge "Enable the quota test cases"