virtualenv_wrapper: Simplify _CHROMITE_DIR discovery.

Based on what we do in constants.py.

BUG=None
TEST=Unittest.

Change-Id: Ic37001b7e6e3c42bb4b95e6a3003b761acdd28a3
Reviewed-on: https://chromium-review.googlesource.com/482526
Commit-Ready: Don Garrett <dgarrett@chromium.org>
Tested-by: Don Garrett <dgarrett@chromium.org>
Reviewed-by: Allen Li <ayatane@chromium.org>
1 file changed