Revert "Remove quota_class params from rest of nova.quota"

This reverts commit d1442a6aec5e1e20cb35627b77739dbe92770e7a.

The quota_classes API was used to set default quota values
so it shouldn't have been removed, so reverting a series
of changes that removed the API and it's internal code.

Related mailing list thread on the topic:

http://lists.openstack.org/pipermail/openstack-dev/2014-May/035383.html

Partial-Bug: #1299517

Change-Id: I839bb6570f5c189e04e284eda8cde7bc2ac29fdb
Merge "Revert "Remove quota_class params from rest of nova.quota""