This introduces a few new redis_* options to simplify the settings
required to use the redis backend. The main aim of this change is to
replace the requirement to inject url by backend_argument.
[cache]
backend=dogpile.cache.redis
redis_server=127.0.0.1:6379
redis_username=default
redis_password=a_big_secret
redis_socket_timeout=1.0
Closes-Bug: #2052351
Change-Id: Id72878f9cddaa99146eab5fb4ee76c8e6a633809
28411250da