logstash: Drop full_message field from GELF messages

The nodejs logging library used by Parsoid and OCG duplicates the whole
message in the 'full_message' attribute.

Change-Id: I9d67fb4c8ca0a32cde07690a7164bce799574b59
logstash: reformat gelf filter config

Add whitespace and hoist comments out of filter blocks to make this
config look more like the udp2log config.

Change-Id: I649eecab2381b5c8f72b8e283faae065b6fe6fed
Merge "logstash: Drop full_message field from GELF messages" into production
Merge "logstash: reformat gelf filter config" into production