Distinguish harness status from subtests in test results view

[foolip]

https://wpt.fyi/results/quirks/classname-query-after-sibling-adoption.html?sha=c0a1bc68d7 looks like this:

https://wpt.fyi/results/visual-viewport/viewport-unscaled-scale-iframe.html?sha=c0a1bc68d7, with harness errors:

(The "File status" misnomer is #419 + #448, should be "Harness status" here.)

Harness statuses aren't passes and failures, but rather a failure to correctly run the test. While harness errors aren't always a serious problem, I believe we should treat them as a separate problem and drive them down close to zero across wpt: web-platform-tests/wpt#10877.

Harness statuses also shouldn't be part of summary numbers, see #62.

Taking this together, I believe we should present them as distinct from subtests. I suggest gray for "OK", and purple (as in #421 (comment)) for anything else. Mockups of the above examples:

[foolip]

Oh, but #449 might not be the issue that fixed the color the first time, I see.