hhvm: make /var/log/hhvm owned by root
On Ubuntu syslog runs as the user 'syslog' but on Debian rsyslog runs as
root and the package does not provide any 'syslog' user.
Since hhvm uses syslog to write to the file, we don't need to make it
accessible to the web user at all. We also change the logrotate and
upstart initscript to be consistent.