Don't try to create the Aphlict log directory if it already exists
Summary: Ref T6944. This was not quite implemented correctly in D11387.
Test Plan: Saw no more exceptions about being unable to create /var/log.
Reviewers: Blessed Reviewers, epriestley
Reviewed By: Blessed Reviewers, epriestley
Subscribers: maxhodak, Korvin, epriestley
Maniphest Tasks: T6944
Differential Revision: https://secure.phabricator.com/D11397