Install python3-zmq on logstash.o.o.

* modules/openstack_project/manifests/logstash.pp: The log-pusher.py
script which feeds jenkins logs into logstash depends on pyzmq for
python3. Install python3-zmq through apt to satisfy this dependency.

Change-Id: Ibd7cec25b865ce93fd8f5ff0c482af2982c68ce8
Reviewed-on: https://review.openstack.org/26406
Reviewed-by: James E. Blair <corvus@inaugust.com>
Approved: Jeremy Stanley <fungi@yuggoth.org>
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Tested-by: Jenkins