Fix for issue where msgpack errors cause modules to be deleted

Right now if there is a deserialization error in msgpack (payload.py) it swallows the exception and returns a dict, this is confusing to the caller since they have no idea that this was an error condition-- which means that the call is indistinguishable from an actual empty dict response. This is manifest mostly in syn
cing files-- because when there is an unpack error the minion assumes that meant
 there where no files on the master, and then just deletes all of its files.

While fixing that I also noticed that the fileclient treats master timeouts the same way (return '', meaning no files). These both seem like bad ideas, in the event a master is unavailable we should error out and just keep the modules that we have.
Remove unused serial object