rename 'notify' to 'trigger_notify'

This is required to make the puppet define work.
- Set the default 'include' metrics to be .*
  This fixes LOGSTASH-968
- Add coverage for LOGSTASH-968
Merge pull request #467 from electrical/change_notify_hipchat

rename 'notify' to 'trigger_notify'
- run more tests
- update filter worker thread safety failure message
Merge git://github.com/logstash/logstash