Check aligned in TestLabelParam webdriver test

[lukebjerring]

Description

Our integration tests should cover the full launch checklist.

This PR adds coverage for:

• /results?label=stable&aligned
• /interop?label=stable&aligned

Checks that the SHAs of the loaded test runs match.

Review Information

make go_firefox_test USE_FRAME_BUFFER=false FIREFOX_PATH=~/browsers/firefox/firefox FLAGS='-test.run=^TestLabel'

and

make go_firefox_test STAGING=true USE_FRAME_BUFFER=false FIREFOX_PATH=~/browsers/firefox/firefox FLAGS='-test.run=^TestLabel'

[Hexcles]

LGTM

[Hexcles]

Tests are failing:

e.g. Chrome: panic: no such element: no such element: Unable to locate element: {"method":"css selector","selector":"wpt-results"}

Firefox also fails a seemingly unrelated test: panic: no such element: Unable to locate element: input.query.

I think Firefox has started to (or will soon) ship native shadow DOM, so we'll need to drop the special case for Firefox when finding shadow elements, but I'm not sure if this is causing the failures.

[lukebjerring]

At a guess, the selenium node package might have bumped their driver versions. FF62 seems to at least pass locally on my machine (both in docker + out of docker). Chrome passes fine outside docker, but not in docker. Guessing that's because my version of the driver on my box is older (ChromeDriver 2.40.565383).

[lukebjerring]

FF seems happy - which means it's flaky. Which isn't newly caused by this PR. I'll merge as-is.