Fix cleanup function to be a bit more robust.

Example failure:
  https://uberchromegw/i/chromeos/builders/whirlwind%20paladin/builds/3673

TBR=akeshet
BUG=chromium:55250
TEST=unit test

Change-Id: I079b11ef90e05e23323010fd92e6527885adacbd
Reviewed-on: https://chromium-review.googlesource.com/311783
Tested-by: David James <davidjames@chromium.org>
Reviewed-by: Fang Deng <fdeng@chromium.org>
1 file changed