Add quota support to Openstack Tenants

Adds support for collecting and storing openstack quota details form various openstack services.

* Adds STI to tenants to support authentication records for tenants
* Adds `cloud_resource_quotas` table and models
    * with STI to support OpenStack specific quotas
* Updates Openstack inventory collection
    * fixes the way that openstack tenants were collected
    * collects quotas based on services and tenants
        - e.g., in Tenant "ABC", the "compute" service allows for 30 vCPUs

Caveats:

* Currently, the Fog library only supports getting quota values based on Tenant.  There's no way to get quota values for specific users through Fog.  This means that Openstack Administrators can only manage quota values available to ManageIQ via the Tenant quota settings, and not the specific quota values associated with the tenant admin user.

This can either be merged as is (after the reviews), or wait until additional support for tenant authentication records is complete.  We can discuss that in the feedback for this PR.

@Fryguy, please review
I think we (the core team) need to discuss which, if any, services should be required.
I require information that's only available through Cinder and I've also encountered similar issues with Glance.
It seems assuming the optional availability of these services will make the implementation of many features very cumbersome.

Maybe we should just put a stake in the ground and state that these services are required for ManageIQ operation.