ZTS: allow alternate work and output dir

[robn]

Motivation and Context

I realised that part of the reason my test rig takes about 15 hours for a full ZTS run is at least in part to do with most of the tests on file vdevs, on ext4, in a VM, on a zvol. Learned a few things, some patches coming soon etc. But the best thing is to just dig out a spare NVMe drive, direct attach it to the VM, and make ZTS use that for everything.

Turns out it's awkward to mount a separate drive at /var/tmp because a typical Linux wants to use that for some of its housekeeping and there's a mild boot ordering issue, so fine, I'll put it somewhere else. But then it turns out that some of the path handling through zfs-tests and test-runner and the tests themselves were a bit messed up, so it wasn't possible to get everything where I wanted it.

So this PR makes it so that if you tell the test runners to use a different path, you get (mostly) get what you pay for. And now all the test work goes to /zts on my test rig, and a full run takes 4 hours, which is very much more manageable.

Description

There's three separate changes here.

First, we make sure that the work dir (default /var/tmp) is threaded through properly. As before, it starts life as $FILEDIR in zfs-tests.sh, settable with -d. That becomes $TEST_BASE_DIR once it hits the test scripts. Some of those had /var/tmp hardcoded, and have been updated. There's also a small handful of setup things like the default vdevs, the constrained_path command dir and the generated runfile for single tests that were also hardcoded, and now go to $FILEDIR.

Next, we remove the explicit outputdir from the runfiles, and properly thread through test-runner's default of /var/tmp/test_results. This was buggy; adding the timestamp suffix was not done consistently for all the different sources of outputdir, so I've fixed that up. Not that we use it, but if the code is going to exist it should probably work right.

Finally, I've made the use of /tmp and $TMPDIR a lot more consistent. In many places, individual tests create work files (including large vdev backing files) using their best guess for a good temporary dir, but it was done very inconsistently and most often ended up with files in /tmp, which I wanted to avoid. So I've made sure $TMPDIR is set to $FILEDIR/$TEST_BASE_DIR, and updated uses of mktemp to use it (usually simplifying the call) and uses of $TMPDIR to use mktemp.

Taken together, this brings the vast majority of the work output under the path specified by the operator in zfs-tests.sh -d, and I'm much happier.

Worth noting that there's still a handful of outputs to /tmp, which I've left for now, mostly because I ran out of day and I'd rather get this posted than leave it lying around for weeks while I find time to finish it off properly.

How Has This Been Tested?

Two successful full ZTS runs completed pointed to an alternate work dir. The handful of tests that were modified for mktemp/$TMPDIR were run directly both on the default /var/tmp and an alternate dir, all passed.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Performance enhancement (non-breaking change which improves efficiency)
• Code cleanup (non-breaking change which makes code smaller or more readable)
• Breaking change (fix or feature that would cause existing functionality to change)
• Library ABI change (libzfs, libzfs_core, libnvpair, libuutil and libzfsbootenv)
• Documentation (a change to man pages or other documentation)

Checklist:

• My code follows the OpenZFS code style requirements.
• I have updated the documentation accordingly.
• I have read the contributing document.
• I have added tests to cover my changes.
• I have run the ZFS Test Suite with this change applied.
• All commit messages are properly formatted and contain Signed-off-by.