Merge remote-tracking branch 'remotes/gkurz-gitlab/tags/9p-fix-2020-11-24' into staging

Mark "local" qtests as slow to avoid unwanted breakage of "make check"
with some configurations (eg. Fedora's Copr automatic build system).

# gpg: Signature made Tue 24 Nov 2020 11:45:14 GMT
# gpg:                using RSA key B4828BAF943140CEF2A3491071D4D5E5822F73D6
# gpg: Good signature from "Greg Kurz <groug@kaod.org>" [full]
# gpg:                 aka "Gregory Kurz <gregory.kurz@free.fr>" [full]
# gpg:                 aka "[jpeg image of size 3330]" [full]
# Primary key fingerprint: B482 8BAF 9431 40CE F2A3  4910 71D4 D5E5 822F 73D6

* remotes/gkurz-gitlab/tags/9p-fix-2020-11-24:
  tests/9pfs: Mark "local" tests as "slow"

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