Update test to use ElasticSearch 2.3.4 as docs says
Update test to use ElasticSearch 2.3.4 as docs says

Searhlight docs and devstack plugin use ES 2.3.4 but the
test-setup.sh file use 2.3.2.

Change-Id: I53d957ac55f20c8ee05937968b38aa46dcd07471
Story: #2003665
Task: #26175

openstack/searchlight,openstack/searchlight,openstack/searchlight