Use Monolog provider for beta logging

Convert the logging configuration for beta from the default
MWLoggerLegacySpi provider to MWLoggerMonologSpi. The Monolog
configuration attempts to preserve the legacy behavior of sending log
events as udp packets to a udp2log service. It also adds handlers that
log directly to logstash via an intermediate redis queue. Once we have
this event stream working reliably we can change the current log2udp
relay rules to exclude MediaWiki events.

With a few more changes on the log event delivery side we should be able
to eliminate the log2udp relay entirely. MediaWiki-Vagrant has
configuration now to accept apache2 and hhvm errors directly via
forwarded rsyslog events. It should be straight forward to replicate
this beta and eventually production.

The udp2log handler configuration still relies on the legacy global
logging variables at this time.

Required MediaWiki changes: I06295cc, If311308
Bug: T845

Change-Id: Ie577bd6a918f52621b942d614f5a917ebf85e6f1