This reverts commit 7d22153d05.
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
Conflicts:
doc/api_samples/all_extensions/extensions-get-resp.json
doc/api_samples/all_extensions/extensions-get-resp.xml
nova/tests/integrated/api_samples/all_extensions/extensions-get-resp.xml.tpl
The conflicts are due to Mark McLoughlin's timestamp-format series
of changes on master (Juno).
Also note that quota_classes.py was changed due to
commit c75a15a4 to rename the NotAuthorized exception
to Forbidden.
Change-Id: I7890e6b41d4ebf19944c1d4db65111fcc4c45463