Add jenkins slave name to the logstash records

zmq publisher already has the computer/node name information
per commit:
openstack-infra/zmq-event-publisher 36ca349

we just need to pull it out of the event and pass it along as
a new field

Change-Id: Iddefdf74ddf170eaafcd82c5e1f5b0389651cf89
Merge "Add jenkins slave name to the logstash records"