Bug 1064646 - Collect static assets and rebuild pyx files before deploy

(see bug)
Chief runs three tasks in sequence - pre_update, update then deploy.
https://github.com/mozilla/chief/blob/master/chief.py#L26

There doesn't appear to be any difference between the steps, other than for readability. ie: adding a method to the end of pre_update() should be the same as adding to the beginning of update().

The rsync happens in checkin_changes() which is called from deploy(), so will be after both pre_update() and update(). I think therefore it makes sense to keep pre_update() to be just about pulling the code, update() to be things like recompiling, clearing *.pyc, updating the DB etc, and deploy() to be just the rsysnc and restarting nodes etc.