Clean up metadata refresh unit test

The stack was not being fully created, because the calls to the mock
functions were not present for the second instance.

Fixes bug #1217829

(cherry picked from commit 0f6e437e889f4a8d7b7c197047a380b04803f3c8)
Conflicts:
	heat/tests/test_metadata_refresh.py

Change-Id: I894473533eb40133e4c22facbbee749a971cec89