[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.
The trick is that I wanna capture the error message that caused the refresh failure.  I suppose I could push that responsibility to the refresher itself.  But, I kinda liked the idea of marking a failed refresh with a single method call.

Maybe this logging would be better suited in EmsRefresh#refresh (https://github.com/ManageIQ/manageiq/blob/master/vmdb/app/models/ems_refresh.rb#L50).  That way, the refresher should simply bail with an exception and allow the EmsRefresh#refresh method to handle logging and setting the refresh status on the EMS.