Make rsyslog forward Apache error log to fluorine

Currently Apache's error log is sent to syslog, which writes it to
/var/log/apache2.log on each application server. This patch makes rsyslog also
forward a copy of each log message to the MediaWiki log aggregator. The logs
are formatted for compatibility with the demuxer on fluorine.

Change-Id: I31c76fdde57c11e58f7b227fb3a87f10f64cf71d
Merge "Make rsyslog forward Apache error log to fluorine" into production