This avoids the (often missing) evaluationDependsOn and fixes using
results from other projects without propagating those through
Configuration. It also reduces the number of useless classes pulled in
by down-stream tests, reducing the probability of rebuilds.
The expectation of fixtures is they help testing down-stream code that
use the classes in main. That applies to all the classes here except for
FakeClock and StaticTestingClassLoader. It would also apply to many
internal classes in grpc-testing, but let's consider cleaning that up
future work.
Eric Anderson