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? 
IMHO, this seems to be bikeshedding. I feel if there are more than 1 server with same name, you can raise/errback custom exception like `SameNameServer` or `ServerMismatch` and fail the launch server job for now. If we (ever) find this error raised in prod, we can then decide what to do.