Only collect accessible openstack tenants.

Openstack admins can see all tenants in an openstack environment.  However, they
only have "access" to tenants to which they've been associated.  If an admin is
only associated to 3 out of 4 tenants in an openstack environment, that admin
can only authenticate against those 3 tenants.

This change restricts our Openstack inventory collection to only gather the
tenant information for the tenants which the EMS user has access.

Note that we still require an admin user to be the EMS user.  If the EMS user is
not an openstack admin in at least one tenant, that user will not be able to
gather other information like tenant quota.
Update openstack refresh vcr cassettes

Needed to account for only getting the "accessible_tenants" from each provider
instead of all tenants.