Move setting the chef-server log level a bit later

While the old place worked, there were two imperfect points:
 - this was located in a code path that is really about picking a
   password for the chef user in rabbitmq
 - this was not executed if rabbitmq already has a chef user
Merge pull request #2058 from vuntz/always-change-loglevel

Move setting the chef-server log level a bit later