Move list stack method to SanityChecksTest class

When sanity stack tests inherits from heatmanager.Heat
class all object are initialized in setup.
So that we send flavor creation request in sanity
list stack tests.
Move list_stack function to the SanityChecksTest class
to avoid post operation and object creation in sanity suit

Change-Id: Ie7c3d7ab9c29d455e42126e37ac9e3ec71fdc26c
Closes-bug: #1297360
Merge "Move list stack method to SanityChecksTest class"