cts: Add a return code indicating timeout
cts: Add a return code indicating timeout

This patch adds CTS_RC_TIMEOUT, which is returned when test
encounters some sort of timeout.

BUG=none
BRANCH=none
TEST=Run cts.py -m i2c. Make buildall

Change-Id: I6d5cbcdde40f24e797e795f30f002da7621d089e
Signed-off-by: Daisuke Nojiri <fd5f93af191bf7e8f73ea71cc3c0f66b41b1dd49@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/393330
Reviewed-by: Randall Spangler <62698fdbb84d1779579ee80c3f39fac22017e5bc@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec