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
These flags are not commonly invoked by users, causing issues when cleaning up old containers. Rather than instruct users to use some random flag, just change the default to what is likely to be more common.
