Migrate build_tar off rules_docker

We want to remove build_tar.py from rules_docker and instead use the one from [rules_pkg](https://github.com/bazelbuild/rules_pkg/blob/master/pkg/build_tar.py).

The two main features we need to add there in order to migrate are:

Xz compression
https://github.com/bazelbuild/rules_docker/pull/433 - added feature
https://github.com/bazelbuild/rules_docker/pull/473 - support for lzma
https://github.com/bazelbuild/rules_docker/pull/636 - toolchains for xz

Debian status file:
https://github.com/bazelbuild/rules_docker/pull/239 - generate per package metadata file

Detailed issues in rules_pkg to address feature parity are:
https://github.com/bazelbuild/rules_pkg/issues/76
https://github.com/bazelbuild/rules_pkg/issues/77