Run tests without constantly restarting the process.

[emilio]

@jgraham mentioned in #6160 that that was one of the blockers, but I don't see any other issue filled for this.

I guess this could be doable now?

cc @jdm @Ms2ger @asajeffrey @aneeshusa @larsbergstrom

[jgraham]

Yeah it seems worth trying again, although it isn't entirely clear if it will produce better performance or acceptable reliability. It should be possible to try wpt with --product=servodriver to see what regressed in the last 18 months or so.

[jdm]

Tests take about 13 minutes to run right now. Even a 50% reduction in time taken would not have a big impact on the overall time taken when building and testing, so I don't feel like investigating this is a big priority right now.