Merge remote-tracking branch 'bonzini/migr-coroutine' into staging

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
* bonzini/migr-coroutine:
  migration: move process_incoming_migration to a coroutine
  migration: handle EAGAIN while reading QEMUFile
  migration: move qemu_fclose to process_incoming_migration
  migration: close socket QEMUFile from socket_close
  migration: xxx_close will only be called once
  migration: use closesocket, not close
  migration: use migrate_fd_close in migrate_fd_cleanup
  migration: clean up server sockets and handlers before invoking process_incoming_migration
  migration: replace qemu_stdio_fd with qemu_get_fd
  migration: add qemu_get_fd
  migration: consolidate QEMUFile methods in a single QEMUFileOps struct
  migration: unify stdio-based QEMUFile operations