Merge remote-tracking branch 'remotes/famz/tags/for-upstream' into staging

Docker testing and shippable patches

Hi Peter,

These are testing and build automation patches:

- Shippable.com powered CI config
- Docker cross build
- Fixes and MAINTAINERS tweaks.

# gpg: Signature made Fri 24 Feb 2017 06:31:10 GMT
# 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/for-upstream:
  docker: Install python2 explicitly in docker image
  MAINTAINERS: merge Build and test automation with Docker tests
  .shippable.yml: new CI provider
  new: debian docker targets for cross-compiling
  tests/docker: add basic user mapping support

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