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? 
I'd be inclined to write this out over several statements. Partially because server_config['server']['metadata'] is the thing we're looking for, but we're iterating over a bunch of servers, so that may be confusing to the casual reader.

And maybe a partial and a filter, but that may just be due to too much clojure for me :)