Merge remote-tracking branch 'bonzini/nbd-next' into staging

* bonzini/nbd-next: (30 commits)
  qmp: add NBD server commands
  block: add close notifiers
  block: prepare code for adding block notifiers
  qemu-sockets: add socket_listen, socket_connect, socket_parse
  tests: do not include tools-obj-y Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
  qemu-sockets: return InetSocketAddress from inet_parse
  qapi: add socket address types
  build: add QAPI files to the tools
  vnc: drop QERR_VNC_SERVER_FAILED
  qemu-sockets: add error propagation to Unix socket functions
  qemu-sockets: add error propagation to inet_parse
  qemu-sockets: add error propagation to inet_dgram_opts
  qemu-sockets: add error propagation to inet_connect_addr
  qemu-sockets: include strerror or gai_strerror output in error messages
  vnc: add error propagation to vnc_display_open
  vnc: reorganize code for reverse mode
  vnc: introduce a single label for error returns
  vnc: avoid Yoda conditionals
  qemu-ga: ask and print error information from qemu-sockets
  nbd: ask and print error information from qemu-sockets
  ...