Merge remote-tracking branch 'remotes/huth-gitlab/tags/pull-request-2021-01-27' into...

Merge remote-tracking branch 'remotes/huth-gitlab/tags/pull-request-2021-01-27' into staging

* Patches to speed up and improve the gitlab-CI
* Documentation for the decorators in the "acceptance" tests
* One small rework of a libqtest function

# gpg: Signature made Wed 27 Jan 2021 06:22:11 GMT
# gpg:                using RSA key 27B88847EEE0250118F3EAB92ED9D774FE702DB5
# gpg:                issuer "thuth@redhat.com"
# gpg: Good signature from "Thomas Huth <th.huth@gmx.de>" [full]
# gpg:                 aka "Thomas Huth <thuth@redhat.com>" [full]
# gpg:                 aka "Thomas Huth <huth@tuxfamily.org>" [full]
# gpg:                 aka "Thomas Huth <th.huth@posteo.de>" [unknown]
# Primary key fingerprint: 27B8 8847 EEE0 2501 18F3  EAB9 2ED9 D774 FE70 2DB5

* remotes/huth-gitlab/tags/pull-request-2021-01-27:
  libqtest: Rework qtest_rsp()
  docs/devel: Explain how acceptance tests can be skipped
  gitlab-ci.yml: Avoid recompiling the sources in the test jobs
  gitlab-ci.yml: Exclude some redundant targets in build-without-default-features
  meson: Do not build optional libraries by default
  configure: Only check for audio drivers if system-mode is selected
  gitlab-ci.yml: Avoid some submodules to speed up the CI a little bit
  gitlab-ci: Test building linux-user targets on CentOS 7
  tests/docker: Install static libc package in CentOS 7

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