Allow timezone attribute

We are currently running into an issue with our Google Compute PubSub where our instances are all using PDT for time but our local Kafka servers are using EST. We would like to be able to specify the timezone of the source logs such that when the data is sent to Kafka the times can be in sync.

Example of file_output plugin here: http://docs.fluentd.org/articles/out_file
See timezone reference in link.