Add SCL channel when registering

@gmcculloug Second of 3 PR's as discussed.
Are you saying the loop only has two items in it?  I think it's a better defensive coding approach to pull that out of the loop regardless of how big it is.  i.e.

```ruby
enabled_repos = LinuxAdmin::RegistrationSystem.enabled_repos
if MiqDatabase.first.update_repo_names.all? { |desired| enabled_repos.include?(desired) }
```