Overhaul the docker support for 2018

<!-- markdown --> This change represents a fairly large overhaul of precommit's Docker support in order to fix many outstanding bugs and feature requests. As a result, there are several incompatible changes from previous versions. Please see the precommit Docker documentation for additional information. End Users: New Features ======================= * Support for pulling a pre-built tag instead of building the base image, platforms, non-standard dockerd socket, and Docker-in-Docker. * `COPY` and `ADD` support when building (requires Docker API version 18+). * All Yetus built images are now labeled with `org.apache.yetus` to make them easier to find via docker inspect. * Docker information in the vote table now properly includes a link to the Dockerfile if URLs, artifacting, etc, are turned on. * Image cleanup should be more reliable. End Users: Incompatible Changes =============================== * The minimum Docker version is now version 17.xx. It was previously 6.xx. * `--dockeronfail` is no longer supported. * `ANT_ARGS`, `ANT_OPTS`, and `MAVEN_OPTS` are now honored. Before they were always overwritten. * `yetus/tp-(number)` images are now removed after normal completion. * Because of the addition of Docker-in-Docker support, Docker mode no longer defaults to privileged mode and the flag has been renamed to be consistent with the other flags. To enable privileged mode, the `--docker-privd` flag must be set to true. Developers: New Features ======================== * `--docker-bash-debug` will run test-patch.sh with `bash -x` inside the container for extensive debugging. * yetuslib now sports a new `yetus_file_to_array` function. Developers: Incompatible Changes ================================ * test-patch.sh's `relative_dir` has been promoted to yetuslib as `yetus_relative_dir` * The internal `ANT_ARGS` has been replaced with `YETUS_ANT_ARGS` * Many changes to how parameters are passed between pre-Docker and post-Docker.