Replaced test_ck_every_* with more interesting error-spam tests

Instead of testing every block (which test_badblocks_every already
does) with a single random bit-error, the new test_ck_spam tests
continuously throw bit-errors at the filesystem until it fails.

This should reveal much more interesting failures than flipping a single
bit in the entire device, while also taking less testing time. And we
still have test_badblocks_every to make sure no specific problem blocks
(except the mrootanchor) are missed.

This makes test_ck_spam more similar to test_exhaustion than
test_badblocks_every.

All this being said, these tests are still sort of in stasis until
rollback protection gets sorted out. So we're not actually testing
anything interesting yet...

I've also reverted the test_badblocks -> test_ck dependency, since we
want to keep the longer-running tests near the end of the queue.

tests/test_badblocks.toml

@@ -7,6 +7,7 @@ after = [
     'test_traversal',
     'test_gc',
     'test_mount',
+    'test_ck',
     'test_compat',
 ]