many tests do not clean up after themselves

[davepacheco]

In the tradition of #499 and #543, this change fixes most of the tests that currently leave detritus in $TMPDIR. I looked into this while looking at #988. Like I said in #543, we could really use a macro like @teisenbe did in #502 but for things that only use a LogContext. I'm not taking that on right now.

This does not fix the internal_dns tests because that's a bunch more work. I filed #990 for that.

I may separately look at having CI fail if a successful run leaves anything in $TMPDIR.

[davepacheco]

As before, I found these by setting TMPDIR to a new directory, then listing it after a successful run:

$ ls -l $TMPDIR
total 108 
drwxr-xr-x   3 dap      staff          3 Apr 28 12:18 internal-dns-test.CRYbrg6MCjrx/
drwxr-xr-x   3 dap      staff          3 Apr 28 12:18 internal-dns-test.jaVVEPleAbdQ/
-rw-r--r--   1 dap      staff       1224 Apr 28 12:18 omicron_nexus-b671045baf67c4da-test_explain_async.15568.16.log
-rw-r--r--   1 dap      staff       1275 Apr 28 12:18 omicron_nexus-b671045baf67c4da-test_explain_full_table_scan.15568.17.log
-rw-r--r--   1 dap      staff       1194 Apr 28 12:18 omicron_nexus-b671045baf67c4da-test_explain.15568.15.log
-rw-r--r--   1 dap      staff      87648 Apr 28 12:18 omicron_nexus-b671045baf67c4da-test_lookup.15568.18.log
-rw-r--r--   1 dap      staff       1350 Apr 28 12:18 omicron_nexus-b671045baf67c4da-test_queries_do_not_require_full_table_scan.15568.5.log
-rw-r--r--   1 dap      staff      28265 Apr 28 12:18 omicron_nexus-b671045baf67c4da-test_region_allocation_is_idempotent.15568.13.log
-rw-r--r--   1 dap      staff      28456 Apr 28 12:18 omicron_nexus-b671045baf67c4da-test_region_allocation_not_enough_datasets.15568.8.log
-rw-r--r--   1 dap      staff      28807 Apr 28 12:18 omicron_nexus-b671045baf67c4da-test_region_allocation_out_of_space_does_not_fail_yet.15568.10.log
-rw-r--r--   1 dap      staff      27813 Apr 28 12:18 omicron_nexus-b671045baf67c4da-test_region_allocation.15568.6.log
-rw-r--r--   1 dap      staff      41970 Apr 28 12:18 test_all-2b010d8188459a74-serial_console_communication.15566.0.log
-rw-r--r--   1 dap      staff      28377 Apr 28 12:18 test_all-2b010d8188459a74-serial_console_communication.15566.1.log
-rw-r--r--   1 dap      staff       5363 Apr 28 12:19 test_all-6cb92dc331378648-test_update_end_to_end.16071.56.log

The file names reflect the names of the tests that created them.