Fix for deletion of nano flavor in OSTF

Add smoke_flavor attribute to setUpClass of SmokeChecksTest
to prevent AttributeError upon tearDownClass invocation
from smoke tests that don`t use it.
Modify HeatBaseTest and TestStackActions classes so that
they support changes.

Change-Id: I33beb5e014781fb12ad45a212f4f81b9d7d324ca
Closes-bug: #1263667