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.
OK.

Floating IPs are tenant-specific (since Networks are tenant specific).

However, I'm not sure either if @network_service.floating_ips will gather all of the floating ips across all tenants.  We can add that into the Network Delegate later if we notice it's not working as expected.