Fix heat ostf-test 'test_autoscaling'

-Autoscaling templates were updated
-Verification that second instance is loaded was changed
(before we counted common number of instances with F17 image and waited until
this number increase, but that's not correct, that's why now we count instances which
belong to test stack and wait for scale-up)

Change-Id: I6c7cecf2f38cb73ef05c6eaea2c958e0cebded5b
Closes-Bug: #1334346