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 Fri 20 Oct 2017 07:30:45 BST
# gpg:                using RSA key 0xCA35624C6A9171C6
# gpg: Good signature from "Fam Zheng <famz@redhat.com>"
# gpg: WARNING: This key is not certified with sufficiently trusted signatures!
# gpg:          It is not certain 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: Fix PATH for ccache
  docker: fix out-of-tree 'make docker-test-build@debian-powerpc-cross'
  docker: allow running from srcdir != builddir build
  docker: cleanup temp directory after test
  docker: Don't allocate tty unless DEBUG=1

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