Delete a quota through admin api.

Added 'extended-quotas' extension that has provides ability for admins
to be able to delete a non-default quota (absolute limit) for a tenant,
so that tenant's quota will revert back to the configured default.

Implements blueprint admin-api-for-delete-quota
Change-Id: I7375420a466823b3e099aebff71a8f7d7f922afb
Merge "Delete a quota through admin api."