Add scale out TCs with availability zone support

Add scale out TCs with availability zone support

Add PROX and vFW scale out TCs with availability zone
configuration. To be able to specify the availability
zone for specific VNF or TG the following example of
command line option shoud be used:

  yardstick -d task start --task-args='{
    "num_vnfs": 2, "availability_zone":
     {
      "vnf_0": "az_0", "tg_0": "az_0",
      "vnf_1": "az_1", "tg_1": "az_1",
      ... }}' <SCALE-OUT-TC-FILE>

The steps to run new scale-out TCs is documented in the
userguide.

JIRA: YARDSTICK-1203

Change-Id: Ib3878485c5483981fe9b48ab02995712bcc31ae5
Signed-off-by: Mytnyk, Volodymyr <volodymyrx.mytnyk@intel.com>