The hashing function for cached backend configuration is different now, so
our hard-coded hash of the HTTP backend address wasn't working anymore.
Here we update the hash so that tests using this test backend will work
again. Rather than leaving it hard-coded, we'll instead compute it the
same way as "terraform init" would.
In practice only one test is actually using this function right now, so
we also update the test fixture for that test (TestPlan_outBackend) to
match the new expectations, though as of this commit it's still failing
with an unrelated error.
c3d11b762b