Provide common code for zeromq filter and output

[suyograo]

logstash-filter-zeromq and logstash-output-zeromq are using utils/zeromq.rb file which was duplicated during beta1 as part of #2055. Previously, before the plugin separation, they shared the same file. We know have to DRY this up to a new plugin like https://github.com/logstash-plugins/logstash-mixin-aws which has common utils code for EC2 input and output.

[jordansissel]

For Logstash 1.5.0, we've moved all plugins to individual repositories, so I have moved this issue to logstash-plugins/logstash-filter-zeromq#5. Let's continue the discussion there! :)