extra/runner: Do not show '404' while the first test is running

It's quite misleading that there is no index.html in the test results
directory until the first test is completed; users new to 'runner'
might think that they entered the wrong address or an error occurred
when they are trying to open the test results.

Generate a row in the table of the index page while a test is running.
It has white background with grey text, and the failure reason is '-'
(empty).

From now on it's not mandatory to execute 'report' with the results
of a completed test, therefore test directories are identified by
the file 'test-name' instead of 'failure-reason'.