v0.7.0: Restructure rules_docker dependency loading (#652)

Features

• Extract transitive dependency defs of rules_docker from container/container.bzl file into a separate file repositories/repositories.bzl. This allows rules loaded in container/container.bzl to use non-Bazel native rules, such as rules from bazel_skylib.

  This change affects how people currently load rules_docker dependencies and rules. For example, to use container_pull rule, in the WORKSPACE, users now need to do:

  load(
      "@io_bazel_rules_docker//repositories:repositories.bzl",
      container_repositories = "repositories",
  )
  container_repositories()
  
  load(
      "@io_bazel_rules_docker//container:container.bzl",
      "container_pull",
  )

  instead of

  load(
      "@io_bazel_rules_docker//container:container.bzl",
      "container_pull",
      container_repositories = "repositories",
  )
  
  container_repositories()

  For more details, please refer to README.md.

• Use incremental loader in container_test (#639)

• Use xz in toolchain (#636)

• Include custom runfile symlinks in layers (#630)

• Make obtainer build user in tests remote execution compatible (#642)

• Support '=' character in path names (#631)

Fixes

• Fix Bazel incompatible issues. (#648)
• Fix container bundle pusher broken by #591 (#651)