[bisection] Make successful build not fan out additional bisection

This is the original behavior that was present in the flutter_engine.py
recipe and I changed it by accident when changing the code to be in a
recipe module.

Change-Id: Iad2d42b89c115def9ceff398f052217f390aaeab
Reviewed-on: https://dart-review.googlesource.com/c/recipes/+/147500
Reviewed-by: Alexander Thomas <athom@google.com>
4 files changed