Tor needs to stop trying to read directories before it changes users
If you use apparmor along with the Tor deb, like pretty much all Ubuntu users, and you want to configure a hidden service, you are in for some misery. For example, let's say your put your hidserv directory in /var/lib/tor/, which would make sense because then Tor will create the directory when it starts, take care of its permissions, etc.
The trouble is that the apparmor rules only let the debian-tor user read stuff in /var/lib/tor. They prevent root from trying to read stuff there (because why should it). But when Tor starts, especially Tor 0.3.0.x, it tries to check all the hidden service directories, as root, before it drops privileges. When apparmor refuses the directory read attempts, Tor flips out and says the config is bad: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=862993
We should audit all of these cases where we try to interact with files and directories before we've dropped privileges, and get rid of the ones we don't need.
(This one is a little bit tricky, because the way we've set up options_validate() vs options_act(), we'd like to be able to detect if a configuration change is going to fail before we commit to it. But I think cleaning up our behavior here is worth having things fail later because of directory problems if they're going to. After all, this way people will be able to use tight and simple apparmor profiles to enforce good behavior inside Tor.)