Ambari repo file (e.g. ambari.repo) should not be required

While it is common to have the repo file be available and even required if Ambari is to be used to add new hosts, for hosted deployments (where users have pre-prepared VM/docker images) the repo file is not necessary. This is because the image usually has ambari components deployed. Add host translates to bringing up a docker/VM instance and starting an agent instance.