Monitor MediaWiki fatals and exceptions in Ganglia

This change extends the EventLogging Puppet module to configure Ganglia
monitoring of MediaWiki fatals and exceptions.

Change I1632a6b19 configured fluorine to forward MediaWiki fatals and
exceptions to vanadium via UDP port 8423. This change configures an
EventLogging UDP-to-ZMQ router that publishes the same stream using ZeroMQ on
TCP 8423. (ZeroMQ facilitates having multiple subscribers consume the stream;
UDP with SO_REUSEADDR does not work well with unicast.)

This change also sets up a metric gathering module that reports errors (broken
down by type) to Ganglia. Error types are detected using simple substring
matching.

Port 8423 is hard-coded in three places (twice in this change, once in
I1632a6b19), which is unfortunate. Instead of plopping static configuration
files in /etc/supervisor, the EventLogging Puppet module should declare
parametrized resource types for common patterns, like UDP-to-ZMQ forwarding.
I intend to do this sometime in the next month or two.

Change-Id: I55450783d018ed7fd7399ee5adf4305af156a59b