extra/runner: Cleanup selftest test_runner_runs_until_failure

Simplify the code by using a file instead of a variable. This file is
created in the $scratchdir (under /tmp) which is deleted if the test
passes. If the test fails then the $scratchdir is kept around until your
system clears out /tmp (typically at the next reboot).
extra/runner: More/better self-tests: {runs_until,continues_after}_failure
extra/runner: selftests: Increase timeout

To avoid false failures when running the tests in parallel. The error
was:

    test_runner_sigint_twice... FAIL
    error: Didn't find 'test.py...' after 1 second

I've also incleased the sleep in `test_runner_sigint_once` to match the
maximum timeout of 2 seconds for each of the `expect_runner_to_say`
calls. And I've increased the sleep in `test_runner_sigint_twice` to an
even larger number to be safe, but in this case it won't increase the
test run-time because the runner should exit after the second `kill`.
extra/runner/report: Improve documentation comment
extra/runner: Add YouView copyright notice