Use Tempest-lib's compute quota_classes_client

Compute quota_classes_client has been migrated to
tempest-lib- I48ce2ddf21218eb02f6ae47cb0356c340ced06ae

Now Tempest-lib provides this client as stable interface so Tempest
should start using this from lib and remove its own copy.
Also remove its unit tests.

This commit makes Tempest to use compute quota_classes_client
from Tempest-lib.

Change-Id: Ibb1d3cbd7d7ffe3a73899f24d315a64fb72e22fe
5 files changed