Otherwise it will inherit the empty python venv.

Bug: 869249
TBR: fbarchard
Change-Id: Ib77d116863f44f482b2cd7cbfaf71966ce2b7629
Reviewed-on: https://chromium-review.googlesource.com/1157535Reviewed-by: Ryan Tseng <hinoka@chromium.org>
Commit-Queue: Ryan Tseng <hinoka@chromium.org>