encryption.innodb_scrub: Clean up. Make it also cover ROW_FORMAT=COMPRESSED,
removing the need for encryption.innodb_scrub_compressed.
Add a FIXME comment saying that we should create a secondary index, to
demonstrate that also undo log pages get scrubbed. Currently that is
not working!

Also clean up encryption.innodb_scrub_background, but keep it disabled,
because the background scrubbing does not work reliably.

Fix both tests so that if something is not scrubbed, the test will be
aborted, so that the data files will be preserved. Allow the tests to
run on Windows as well.