As 284, part 1 - find a created server on Nova (ready for review)

This change is bigger than I thought, so I am trying to break it up into bits.  This part just provides the functionality to check Nova for an exact server that matches a given server config, created around a certain time.

Question for the next part - should we wait at all after getting a 500 or 401 response back from Nova from creating a server, before checking Nova to see if a server was created? 
It probably wouldn't hurt, but as long as the SUT documents it I guess it's fine? Plus there's other places you'd have to repeat the comment :) I think it's fine either way, up to you :)