Add a System test vCenter + VLanManager HA-mode

- implement following testing scenario:
  * create HA cluster
  * add 2 controllers and 1 controller+cinder node
  * configure Nova VLanManager
  * deploy aforementioned nodes in one go
  * run network test
  * run OSTF

Related: blueprint vcenter-vlan-manager
Change-Id: Iae459e7a032bb2171b22ebc0f8c7ab630d284146
Merge "Add a System test vCenter + VLanManager HA-mode"