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.
@roliveri IIRC when you re-record the cassette and some of the parameters have changed (vm count for instance) and you have ``` :allow_unused_http_interactions => false ``` it eats all errors and rather than getting something like "expected vm.count to eq 17, got 42" you just get "you have unused transactions".