extra/runner report: 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 being
executed. It has white background with grey text, and the exit status
is "still running".

This is done by skipping `report` if it's run with no arguments or
--classify-only and no exit-status is found in the test run directory,
but executing it if it's run with --html-only.
extra/runner summary report: Display the plot when no passed test

jqplot has a limitation that it considers the data set passed to its
constructor invalid if `plotSeries[0]` is an empty array, which is
the case when no completed tests passed.

Work around this limitation by passing `null` to `plotSeries[0]`
before the constructor is invoked, and removing the fake element
afterwards. It's only the constructor that has the limitation,
`plot1.replot()` is working fine if `plotSeries[0]` is empty.
extra/runner summary report: Remove dash from exit status "still running -"
extra/runner report: Don't show details pane for "still running" test

This makes the row of the test non-clickable, and skipped by the up/down
arrow keyboard navigation.

Reasons:

- The page doesn't contain any valuable information until the testrun
  has completed.
- The user mustn't hide the page with the "[Hide this result]" link.
Merge branch 'runner-to-add-index-page-at-start'

* runner-to-add-index-page-at-start:
  extra/runner report: Don't show details pane for "still running" test
  extra/runner summary report: Remove dash from exit status "still running -"
  extra/runner summary report: Display the plot when no passed test
  extra/runner report: Do not show "404" while the first test is running