web: convert messages to string before calling force_encoding
web: convert messages to string before calling force_encoding

when sending messages as JSON, the event.message corresponds to a java
HashMap - which knows nothing of force_encoding.  Make sure to flatten
it to a string before making sure its UTF8.

joekiller/logstash-kafka,opentable/logstash-kafka,tinglinux/logstash-kafka,opentable/logstash-kafka,Aloomaio/logstash-kafka,tinglinux/logstash-kafka,Aloomaio/logstash-kafka,joekiller/logstash-kafka