misc: localize logged GatherRunner error

[brendankenny]

another tiny one, apologies for the spam :)

Right now when you hit a pageLoadError you get a logged message like
GatherRunner:error lighthouse-core/lib/lh-error.js | pageLoadFailedInsecure # 0 https://expired.badssl.com/ +3ms

This gets the full string for it.

fixes #8944 edit: nope

[connorjclark]

fixes #8944

[patrickhulce]

LGTM

[patrickhulce]

need to fix some test failures though

[brendankenny]

need to fix some test failures though

ok, the test fixes are a little large, but I think help things. They don't overlap with the original commit but may be easier to review as a separate commit (e447753).

The root cause was that those two failing tests were using mocked settings which didn't have a locale, so it was trying to do a lookup in LOCALES[undefined] for the newly localized error message. I updated the two tests to use real configs because that's super easy and the default settings (with a real locale) are there by default then.

I also updated the error message you get when you ask for an invalid locale (like LOCALES[undefined]) since the current error isn't very helpful, then added two simple i18n-test.js tests for the updated error string.

You should probably take another look @patrickhulce :)

[brendankenny]

this isn't something that should ever happen outside of tests since in a normal run we specifically pick which locale to use from the keys of LOCALES itself.

...but if it does somehow happen in a normal run, this is a strictly better error message than "Cannot read property 'lighthouse-core/lib/lh-error.js | pageLoadFailed' of undefined" anyways, so seems ok.

[patrickhulce]

turned into a different change haha but still LGTM!