This makes the installation a bit more secure by ensuring a user does not accidentally expose a way for unauthorized users to add new ssh keys to the system.
Additionally, this removes the extra HOSTNAME file to make the initial install process easier (that file was not modifiable by any dokku commands.
Closes#2247
The default for an app is empty, meaning it will fallback to the global value (which defaults to true). This will allow users to properly override the global value, regardless of what it is.
