Merge remote-tracking branch 'remotes/stsquad/tags/pull-travis-speedup-090218-1' into staging

One patch to mitigate Travis timeouts

# gpg: Signature made Fri 09 Feb 2018 14:13:46 GMT
# gpg:                using RSA key FBD0DB095A9E2A44
# gpg: Good signature from "Alex Bennée (Master Work Key) <alex.bennee@linaro.org>"
# Primary key fingerprint: 6685 AE99 E751 67BC AFC8  DF35 FBD0 DB09 5A9E 2A44

* remotes/stsquad/tags/pull-travis-speedup-090218-1:
  .travis.yml: add --disable-linux-user for some jobs

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