Remove redundant _stack_rand_name from func tests

Base HeatIntegrationTest class uses _stack_rand_name method in
stack_create method, so redundant using of _stack_rand_name should be removed
in tests, where:
 1. stacks.create method is not called directly
 2. stacks_name is not used later in the test

Change-Id: Iabdd945604a8276b33930b264689c3a2edadecd8
3 files changed
tree: ad14c8014c1b240102eb763af8b670dbd4e2ce8c
  1. common/
  2. functional/
  3. scenario/