The variable 'interval' is declared as unsigned integer, and this
sometimes causes an integer underflow when substracting it by SECOND,
and in turns leads to false test failure. Changing it to signed integer.
BUG=chrome-os-partner:19236
TEST=Repeatedly run hooks test
BRANCH=None
Change-Id: Ic6d8001f90fb8756b6bdadf811a668c02fbccb34
Signed-off-by: Vic (Chun-Ju) Yang <victoryang@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/181882
Reviewed-by: Vincent Palatin <vpalatin@chromium.org>