test: Run unit tests on windows bazel build (googleapis/google-cloud-cpp-spanner#475)
test: Run unit tests on windows bazel build (googleapis/google-cloud-cpp-spanner#475)

* test: Run unit tests on windows bazel build

* Fix unit test on windows

googleapis/google-cloud-cpp,googleapis/google-cloud-cpp,googleapis/google-cloud-cpp,googleapis/google-cloud-cpp