Merge remote-tracking branch 'remotes/stsquad/tags/pull-testing-040320-1' into staging

Testing updates

  - some clean-ups for tests/vm
  - enable tools build for MacOSX
  - bump avocado to a newer version
  - bump travis env for avocado

# gpg: Signature made Wed 04 Mar 2020 10:00:19 GMT
# gpg:                using RSA key 6685AE99E75167BCAFC8DF35FBD0DB095A9E2A44
# gpg: Good signature from "Alex Bennée (Master Work Key) <alex.bennee@linaro.org>" [full]
# Primary key fingerprint: 6685 AE99 E751 67BC AFC8  DF35 FBD0 DB09 5A9E 2A44

* remotes/stsquad/tags/pull-testing-040320-1:
  travis.yml: install python3 numpy and opencv libraries
  tests/acceptance: bump avocado requirements to 76.0
  configure: detect and report genisoimage
  travis: enable tools build on OS X
  tests/vm: Added gen_cloud_init_iso() to basevm.py
  tests/vm: give wait_ssh() option to wait for root
  tests/vm: increased max timeout for vm boot.
  tests/vm: Debug mode shows ssh output.
  tests/vm: use $(PYTHON) consistently

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