This correctly generates 'use_bbagent' in luci.recipe().

R=nodir@chromium.org, vadimsh@chromium.org, yiwzhang@google.com

Bug: 1015181
Change-Id: I7a0b0086a98600fd7429434ab244d82b58efa2d8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2216540
Commit-Queue: Robbie Iannucci <iannucci@chromium.org>
Commit-Queue: Andrii Shyshkalov <tandrii@google.com>
Commit-Queue: Vadim Shtayura <vadimsh@chromium.org>
Auto-Submit: Robbie Iannucci <iannucci@chromium.org>
Reviewed-by: Andrii Shyshkalov <tandrii@google.com>
Reviewed-by: Vadim Shtayura <vadimsh@chromium.org>
Reviewed-by: Yiwei Zhang <yiwzhang@google.com>