Make stack complete depend on all nodes

Previously the completion signal was just based on the first run of
os-refresh-config. But in this case, we actually need to wait until it
runs successfully with all hosts computed. That way we can know that
services aren't in an unstable state while that configuration rolls out.

Change-Id: I3b965c19c92b366df3069cb8e1daffa18252c884
Closes-Bug: #1337230