Don't try to automatically alter system_auth replication parameters

[a1exsh]

This proven to be dangerous in some migration scenarios, and we need to do this exactly once. Instead of trying to do it on every startup and hoping it will fail if already done, just instruct the user to do it manually after creating a cluster.

[slitsche]

Could also update the README.rst?

[a1exsh]

:+1:

[slitsche]

👍