xfstests: deprecate busted log printing tests

xfstests: deprecate busted log printing tests

Tests 018, 081 and 082 read the contents of the log and assume that the
contents will always be the same. They are trying to ensure that the
contents of the log don't change for a given fixed load.

This has several problems - high level changes to the filesystem and
VFS code can change the order and contents of the log. Changes to
the way we sync the filesystem will change the contents of the log.
background writeback occurring in the middle of the test will change
the contents of the log by allowing the tail to move. Even changes
to the default mkfs parameters can break them!

The tests also assume that unmount leaves a dirty log behind. We've
fixed lots of problems in sync and the unmount paths over recent
times, so now a clean unmount leaves a clean log behind. That is,
there is nothing left in the log print output for these tests to
check. IOWs, major surgery is required for these tests to be
returned to their former break-when-something-changes behaviour.

However, these tests are a maintenance nightmare. They spend more
time broken and failing than they do passing, and then it's not long
before they get broken again. They have to cover all sorts of
different permutations of log configurations and that will continue
to grow and increase the complexity of making these tests continue
to work. And to top it all off, I can't remember a bug actually ever
being found by these tests. Hence I think we should just stop using
them altogether.

So this patch deprecates 018, 081 and 082 rather than fixes them.
It introduces a "deprecated" test group and puts them in it. That
means the tests can still be run on older systems where they may
have some use, but will not be run automatically any more, nor
will any attempt be made to keep them up to date or working.

Signed-off-by: Dave Chinner <david@fromorbit.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>