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.
After you get "you have unused transactions" then you re-record the cassette. Then you'll get "expected vm.count to eq 17, got 42". You shouldn't get "you have unused transactions" after re-recording the cassette, unless there's a caching issue with multiple iteration tests.