Add way to delete users

[mrjones-plip]

Right now if you get a big list of users for your org and then 3 months later regenerate this list of users, any users that have left your org and are not in the user.txt file stick around and still can use the service.

We should allow a --delete flag or something to be passed in such that any user not in the user.txt file is deleted (vhost, TLS cert, login, home dir etc.)