explore a bazel ACI build output

[jonboulle]

Google recently released the Bazel build tool. A lot of its goals and features (reproducibility, speed, static/self-contained builds) are very closely aligned with what we're trying to achieve with the App Container Spec. We should explore using Bazel to build ACIs, potentially via Skylark. First step is probably to just reach out on the bazel mailing list for advice.