This test would previously fail randomly due to the use of multiple
resource instances. Instance keys are iterated over as a map for
presentation, which has intentionally inconsistent ordering.
To fix this, I changed the test to use different resource addresses for
the three drift cases. I also extracted them to a separate test, and
tweaked the test helper functions to reduce the number of fatal exit
points, to make failed test debugging easier.
c51112a30c