Respect .gitignore when cleaning checkout

dup_it_worker was blowing away the output logs folder because we asked
it to ignore the .gitignore rules.

BUG=chromium:724619
TEST=None

Change-Id: I0a610b1403d753f7282618191b2d38c28fa33feb
Reviewed-on: https://chromium-review.googlesource.com/518984
Reviewed-by: Prathmesh Prabhu <pprabhu@chromium.org>
Tested-by: Prathmesh Prabhu <pprabhu@chromium.org>
1 file changed