Drush does not work after I sudo su to another user
Found the answer here:
https://superuser.com/questions/453988/whats-the-difference-between-su-with-and-without-hyphen


  The difference between "-" and "no hyphen" is that the latter keeps
  your existing environment (variables, etc); the former creates a new
  environment (with the settings of the actual user, not your own).