platform_HWwatchdog: Handle watchdog timeout dynamically

Rather than hardcoding that a watchdog reboot will happen in 30
seconds, query the watchdog to see when the timeout will happen.

BUG=chromium:326608
TEST=platform_HWwatchdog
TEST=Comment out "self.client.run('echo "z" > %s' % wd_dev);" and
platform_HWwatchdog now fails.

Change-Id: Ia8961439414273923fabb9d66a983a94bf68cccf
Signed-off-by: Doug Anderson <dianders@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/179288
Reviewed-by: Grant Grundler <grundler@chromium.org>
1 file changed