update keystone.conf to Icehouse

- Added a lot of `oslo.messaging` attributes which are unused around
  `amqp`, `rabbitmq`, `kombu`. `rpc_backend` now defaults to rabbitmq instead
  of kombu (but we were never changing this value)

- [auth].methods changed default from `external,password,token,oauth1`
  to `external,password,token`. This was set explicitly in our config,
  but I think it was only because that's how it used to be in Havana as
  we weren't using (or configuring) oauth1.

- A lot of the config options which we were hardcoding are now
  defaults (and commented in the sample config). These were left
  commented like upstream:
  * [auth].password/token/oauth1
  * [catalog].driver
  * [ec2].driver
  * [paste_deploy].config_file
  * [policy].driver