Fix database poison warnings in resource providers
Fix database poison warnings in resource providers

The introduction of the _ensure_rc_cache method in lots of places
has caused new database poison errors in test_resource_provider.py.

This changes fixes those issues by mocking the call to _ensure_rc_cache
and the id_from_string/string_from_id methods of the cache object.

Co-Authored-By: Ed Leafe <a162caffcb6897220f4d1cf28164d73cb91993a8@leafe.com>
Related-Bug: #1568414
Change-Id: Ib8828544772a6e738e43f20591c795d2ef9bf901

phenoxim/nova,vmturbo/nova,openstack/nova,hanlind/nova,gooddata/openstack-nova,mahak/nova,jianghuaw/nova,Juniper/nova,rajalokan/nova,rajalokan/nova,gooddata/openstack-nova,klmitch/nova,rahulunair/nova,openstack/nova,mahak/nova,hanlind/nova,Juniper/nova,klmitch/nova,Juniper/nova,vmturbo/nova,Juniper/nova,openstack/nova,jianghuaw/nova,mikalstill/nova,hanlind/nova,klmitch/nova,rahulunair/nova,rajalokan/nova,rajalokan/nova,mahak/nova,phenoxim/nova,jianghuaw/nova,rahulunair/nova,vmturbo/nova,mikalstill/nova,vmturbo/nova,klmitch/nova,jianghuaw/nova,gooddata/openstack-nova,mikalstill/nova,gooddata/openstack-nova