tests: Cleanup and warn about unfinished SIGALRM (fix tests that don't cleanup)

Because the lava_dispatcher code uses SIGALRM for timeouts it is important that there shouldn't be any dangling SIGALRM scheduled after running a test. Otherwise the next test might fail because the SIGALRM will raise an exception scheduled in the previous test.

Also emit a warning so that offending tests can be fixed.

Fix all tests that did not cleanup properly.