Right after setup_heat_network.sh deletes the test stack, we shut down
the controller node for a snapshot. This opens a race: the controller
node may never actually delete the heat stack. The test stack stays
in the system, using up the space the test script, launch_instance.sh
needs for its instance VM.
With this patch, setup_heat_network.sh waits for the test stack to
disappear.
Change-Id: I23241998a40b904ef9c26717619e66d4377ce6f9
850bddb63d