Beta: use redis for session storage

Antoine's change I5e1a32428 said "one day [we] will have to use redis instead".
Today is the day. There is no reason for Labs to diverge from production in its
choice of storage backend for session storage.

Also update the IP of deployment-redis01.

Change-Id: I6728aab0c95bb1fa8c801f233734fac443b8d374
Merge "Beta: use redis for session storage"