This test was using old-style state files as its input, differing only by
lineage. Since lineages are now managed within the state manager itself,
the test can't use that to distinguish the two files and so we put a
different output in each one instead.

This also introduces some TRACE logging to the migration codepaths.
There's some hard-to-follow control flow here and so this extra logging
helps to understand the reason for a particular outcome, and since this
codepath is visited only in "terraform init" anyway it doesn't hurt to
be a bit more verbose here.