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: I5eff4821887e851788f55ad8dfdc62fa4f615d11
Closes-bug: #1263667