It was confusing because there are two concepts with the same name:
thebootstrapping config special-cased in the bootstrap modules /
singletons and the "global" config.
This change folds the first into the second.
A further next step would be to split the Go parts and the Ninja parts
(subninjas + primary builder invocation) apart, but at some point, I
should stop gold-plating this.
Test: Presubmits.
Change-Id: Id341dee664a9d2527535f4f9980e5f0d10139eef
d782b504e0