Merge remote-tracking branch 'remotes/stsquad/tags/pull-misc-for-rc0-150720-3' into staging

Final fixes for 5.1-rc0

  - minor documentation nit
  - docker.py bootstrap fixes
  - tweak containers.yml wildcards
  - fix float16 nan detection
  - conditional use of -Wpsabi
  - fix missing iotlb data for plugins
  - proper locking for helper based bb count
  - drop ppc64abi32 from the plugin check-tcg test

# gpg: Signature made Wed 15 Jul 2020 11:59:08 BST
# 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-misc-for-rc0-150720-3:
  .travis.yml: skip ppc64abi32-linux-user with plugins
  plugins: expand the bb plugin to be thread safe and track per-cpu
  cputlb: ensure we save the IOTLB data in case of reset
  tests/plugins: don't unconditionally add -Wpsabi
  fpu/softfloat: fix up float16 nan recognition
  gitlab-ci/containers: Add missing wildcard where we should look for changes
  docker.py: fix fetching of FROM layers
  tests/docker: Remove the libssh workaround from the ubuntu 20.04 image
  docs/devel: fix grammar in multi-thread-tcg

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