Avoid =~ since msysgit bash doesn't support it.
Avoid =~ since msysgit bash doesn't support it.

This uses grep instead.  Note that just grepping for "--force" matches other
things, e.g. "foo--force--foo", but that's a problem with the original code as
well, I think.

BUG=435729
TEST=Run gclient under msysgit bash.  No error should occur.

Review URL: https://codereview.chromium.org/789353002

git-svn-id: bd64dd6fa6f3f0ed0c0666d1018379882b742947@293340 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

svn2github/chromium-depot-tools,svn2github/chromium-depot-tools,svn2github/chromium-depot-tools