Comment 1 for bug 1615983

I'm not sure we can solve this in time for the newton release, it's something we'll have to document (e.g in the matrix of services, certain services can only be deployed on exactly one role), then we can look at some more flexible approach during Ocata (which will enable e.g scaling out to add some more aodh-api nodes while leaving the current services running on the ControllerRole.