Merge remote-tracking branch 'remotes/famz/tags/docker-pull-request' into staging

Merge remote-tracking branch 'remotes/famz/tags/docker-pull-request' into staging

# gpg: Signature made Wed 20 Jul 2016 12:19:56 BST
# gpg:                using RSA key 0xCA35624C6A9171C6
# gpg: Good signature from "Fam Zheng <famz@redhat.com>"
# gpg: WARNING: This key is not certified with a trusted signature!
# gpg:          There is no indication that the signature belongs to the owner.
# Primary key fingerprint: 5003 7CB7 9706 0F76 F021  AD56 CA35 624C 6A91 71C6

* remotes/famz/tags/docker-pull-request:
  docker: pass EXECUTABLE to build script
  docker: Don't start a container that doesn't exist
  docker: Add "images" subcommand to docker.py
  docker: Fix exit code if $CMD failed
  docker: More sensible run script
  tests/docker/docker.py: add update operation
  tests/docker/dockerfiles: new debian-bootstrap.docker
  tests/docker/docker.py: check and run .pre script
  tests/docker/docker.py: support --include-executable
  tests/docker/docker.py: docker_dir outside build

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>