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.
Not knowing much about the `delegate` ruby lib or `DelegateClass`, the name `dobj` was confusing here.  Could you consider `delegate` as the name of the delegated object instead of the abbreviated `dobj`?