[WIP] Ems refresh status

Capture the status of an EMS Refresh (success or failure).

Currently captures the status for Openstack.  Need to look at adding this either the refresher super class or to each individual provider's refresher.
I'm not sure I like this approach to setting the refresh status.  It's weird having to call a method to set a value when the method looks like a predicate method.  Something that seems clearer to me would be to just overload `refresh_status=` and have hard values in a validator.