tests/watchdog: Add a helper for counting down with the watchdog

This reduces a bunch of duplicate code that loops through an event loop
to try and guage how long it took for the watchdog to expire.

Change-Id: Ib3b33e250b157df02eff39751277c564ea40705c
Signed-off-by: William A. Kennington III <wak@google.com>
2 files changed