Add test for simple deployment with zabbix

Includes:
* turn on experimental mode
* restart nailgun
* check that new role appears
* deploy cluster
* run ostf
* get zabbix url
* login in dashboard, get events

Change-Id: I4d32bd19691e465ba4529c11ccd1e12a2091284e
Implements-blueprint: implement-tests-for-monitoring-system
(cherry picked from commit 18b6f563024972f0d3a710d1d7eaedf766f60628)