Per-project-user-quotas for more granularity

Implements blueprint per-user-quotas.

Fixes bug 968175

Based on the original quotas structure.

NOTE:
quota_instances, quota_cores, quota_ram, quota_key_pairs and
quota_security_groups are supported per user.

Add CRUD methods for project user quotas API. DocImpact
 - Shows quotas for a user.
   GET v2/{tenant_id}/os-quota-sets/{tenant_id}?user_id={user_id}
 - Updates quotas for a user.
   POST v2/{tenant_id}/os-quota-sets/{tenant_id}?user_id={user_id}

Add commands for project user quotas management.
 - Show user quotas:
   nova-manage project quota --project <Project name> --user <User name>
 - Update/Create user quotas:
   nova-manage project quota --project <Project name> --user <User name>
   --key <key> --value <value>

Change-Id: I24af1f6bc439d5d740303c6fe176a9bffe754579
Merge "Per-project-user-quotas for more granularity"