Previously, any t_skip would cause the final test result to be a failure
because up until now no test should have been skipped.
However, with format-version-forward-back not being compatible with el9,
we are going to rely on el7/8 testing for that test soleley, and
therefore we have to allow skipping of this test on el9 and newer OS
versions.
We add `t_skip_permitted` to signal this from the test case to the
run-tests.sh script. A new exit code is passed, and all accounting is
updated to reflect that a test was skipped, but this was permitted. We
modify format-version-forward-back to use this new exit path.
Signed-off-by: Auke Kok <auke.kok@versity.com>
fc7876e844