Add logrotate for the phabricator logs.

They've gotten very big over time!

   $ ls -lh ~/logs/phab*
   -rw-r--r-- 1 www-data root     603M Nov 26 13:51 /home/ubuntu/logs/phabricator-access.log
   -rw-r--r-- 1 www-data www-data 1.5G Nov 26 13:51 /home/ubuntu/logs/phabricator.log

This should help keep them in check.

Auditors: chris

Test Plan:
Fingers crossed.  Will install this on the phabricator machine and
check the logs tomorrow.