Python source reorganization.

...e/testing/blocking_invocation_inline_service_test_case.py

src/python/src/grpc/framework/face/testing/callback.py

src/python/src/grpc/framework/face/testing/control.py

src/python/src/grpc/framework/face/testing/coverage.py

src/python/src/grpc/framework/face/testing/digest.py

...g/event_invocation_synchronous_event_service_test_case.py

...future_invocation_asynchronous_event_service_test_case.py

src/python/src/grpc/framework/face/testing/interfaces.py

src/python/src/grpc/framework/face/testing/serial.py

src/python/src/grpc/framework/face/testing/service.py

src/python/src/grpc/framework/face/testing/stock_service.py

src/python/src/grpc/framework/face/testing/test_case.py

src/python/src/grpc/framework/foundation/__init__.py

src/python/src/grpc/framework/foundation/_later_test.py

...ython/src/grpc/framework/foundation/_logging_pool_test.py

src/python/src/grpc/framework/foundation/_timer_future.py

src/python/src/grpc/framework/foundation/abandonment.py

src/python/src/grpc/framework/foundation/callable_util.py

src/python/src/grpc/framework/foundation/future.py

src/python/src/grpc/framework/foundation/later.py