Fixed RTD documentation generation

Fixed output for
http://magnetodb.readthedocs.org/en/latest/

Change-Id: I4d6bf3aa5f6b8a076d8e458d5571cea0a594751b
Add rate limiting per tenant

Add rate limiting per tenant per single node,
or per gunicorn worker in gunicorn enabled configuration

Implements blueprint: rate-limit-per-tenant

Change-Id: Ib8b39e94a74977f9b8174be686d4810c05ad7e0a