Failure notification in different room

This PR is based on #206 
We wanted to give failures a bit more visibility by having them post to general instead of just the danger room.
The Notifier::FailureService is basically the sames as the ChatService, but it will use the room id set in the `JANKY_CHAT_FAILURE_ROOM` environment variable. It won't do anything if it is not set.
I think would be beter if to these three checks were wrapped into their own method, something like
```ruby
def need_failure_notification?(build)
  !build.green? && ENV["JANKY_CHAT_FAILURE_ROOM"] != build.room_id
end
```