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.
Do you mean for floating_ips? I think we may need to implement that. I couldn't verify because our Havana environment (that has nova) only has one tenant configured. I didn't want to mess with that environment until after this was merged. Why break the tests all at once, when you can do it a piece at a time.