Merge remote-tracking branch 'remotes/armbru/tags/pull-yank-2021-01-13' into staging

Yank patches patches for 2021-01-13

# gpg: Signature made Wed 13 Jan 2021 09:25:46 GMT
# gpg:                using RSA key 354BC8B3D7EB2A6B68674E5F3870B400EB918653
# gpg:                issuer "armbru@redhat.com"
# gpg: Good signature from "Markus Armbruster <armbru@redhat.com>" [full]
# gpg:                 aka "Markus Armbruster <armbru@pond.sub.org>" [full]
# Primary key fingerprint: 354B C8B3 D7EB 2A6B 6867  4E5F 3870 B400 EB91 8653

* remotes/armbru/tags/pull-yank-2021-01-13:
  tests/test-char.c: Wait for the chardev to connect in char_socket_client_dupid_test
  io: Document qmp oob suitability of qio_channel_shutdown and io_shutdown
  io/channel-tls.c: make qio_channel_tls_shutdown thread-safe
  migration: Add yank feature
  chardev/char-socket.c: Add yank feature
  block/nbd.c: Add yank feature
  Introduce yank feature

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