Replace usage of setTimeout with step_timeout in old-tests/webdriver (#4969)

This is expected to help test stability on slow configurations, as the
timeouts will be multiplied by the timeout multiplier.

Split out from #1816.

View on GitHub: https://github.com/w3c/web-platform-tests/pull/4969

Received on Wednesday, 22 February 2017 17:15:24 UTC