recipes_test.py: Use recipe bootstrap
recipes_test.py: Use recipe bootstrap

This ensures coverage is installed, rather than depending on it being
installed in your system.

BUG=671189

Change-Id: Id9d7c514b4db53963381c5269bee06c706b23751
Reviewed-on: https://chromium-review.googlesource.com/442050
Commit-Queue: Stephen Martinis <f3fbe4c4218d2421400bf0bd07366865fd7a0c7e@chromium.org>
Reviewed-by: Robbie Iannucci <40f3d43a28ebae3cb819288542e1c84d73d962d5@chromium.org>

CoherentLabs/depot_tools,CoherentLabs/depot_tools