OpenStack - Ensure inventory is collected for all tenants.

@Fryguy @blomquisg please review.

For OpenStack refresh, ensure inventory is collected for all of the
tenants the EMS can access.

Extended OpenstackHandle to include tenant iterators.
Updated EmsOpenstack and the openstack parser to use the OpenstackHandle accordingly.
Updated spec tests and rerecorded vcr cassettes.
Yes, I need to account for this. I don't think it should be set per-connection. I'm thinking it should be set when the OpenstackHandle object is instantiated. It would then apply to all the connections made through the handle.