Add quota support to Openstack Tenants

Adds support for collecting and storing openstack quota details form various openstack services.

Backend updates:
* 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

UI Updates:
* Tenant tab in Cloud subnav
* Cloud Tenants in Openstack provider relationships lists (listnav and textual summary)
* Security Groups, Instances, and Images relationships for Tenant summary page
* Quota on Tenant summary page

NB:  Rebased this PR to remove the references to the Tenant Auth support.  I've got that stashed away as a separate branch for now.  If it turns out we still need that concept, we can go back to it.  For more information, see @roliveri's comments on outdated diffs below.

@Fryguy, @roliveri, @dclarizio, @h-kataria please review
Yes indeed!

But, have a quick peek at that file overall.  It's littered with copy/paste reuse.  Unfortunately, this change perpetuates that.  But, refactoring this file then hiding my change in that refactoring would make it extremely hard to review this small change.

The flip side is that attempting to review this change in its current form is difficult because of how verbose everything is in this file.

Nonetheless, I think I would like to leave it like this in order to follow the surrounding style.  We will need to have a separate effort to clean this up that doesn't also introduce functional changes.