Merge remote-tracking branch 'remotes/famz/tags/pull-docker-20160601' into staging

v2: Fix warning due to include.
    Various temp dir/file changes.
    Don't use "find -executable" to be compatible with Mac.

# gpg: Signature made Wed 01 Jun 2016 10:30:33 BST using RSA key ID 6A9171C6
# 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/pull-docker-20160601:
  .gitignore: Ignore docker source copy
  MAINTAINERS: Add tests/docker
  docker: Add EXTRA_CONFIGURE_OPTS
  docs: Add text for tests/docker in build-system.txt
  docker: Add travis tool
  docker: Add mingw test
  docker: Add clang test
  docker: Add full test
  docker: Add quick test
  docker: Add common.rc
  docker: Add test runner
  docker: Add images
  Makefile: Rules for docker testing
  Makefile: Always include rules.mak
  rules.mak: Add "COMMA" constant
  tests: Add utilities for docker testing

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