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.
Actually, I don't think there's a simple term for the incoming object.
In English terms:
- Delegator(n) - the entity assigning a delegate - so that would be the code instantiating the delegate class.
- Delegate(v) - to assign an entity to act on behalf of another.
- Delegate(n) - an entity that acts on behalf of another - that would be the object instantiated from the delegate class.

The incoming object is the object being acted on behalf of by the delegate. I'm not sure what it should be called. Initially, I was thinking "delegatee" but I think that's a synonym for delegate(n).
So:
A delegator delegates  a delegate to act on behalf of [whatever that incoming object is called].

:-)