uvt-kvm wait for vivid or xenial VMs doesn't work on a trusty host

uvt-kvm wait works correctly on a xenial host. But on a trusty host, it never returns when creating vivid or xenial VMs:

will@host:~$ date
Thu Aug 18 22:44:27 NZST 2016
will@host:~$ sudo uvt-kvm create --cpu 8 --memory 2048 --disk 8 --ssh-public-key-file ~will/.ssh/authorized_keys waitdemo arch=amd64 release=trusty
will@host:~$ uvt-kvm wait --insecure waitdemo
Warning: Permanently added '192.168.122.215' (ECDSA) to the list of known hosts.
will@host:~$ sudo uvt-kvm destroy waitdemo
will@host:~$
will@host:~$ date
Thu Aug 18 22:44:40 NZST 2016
will@host:~$ sudo uvt-kvm create --cpu 8 --memory 2048 --disk 8 --ssh-public-key-file ~will/.ssh/authorized_keys waitdemo arch=amd64 release=utopic
will@host:~$ uvt-kvm wait --insecure waitdemo
Warning: Permanently added '192.168.122.185' (ECDSA) to the list of known hosts.
will@host:~$ sudo uvt-kvm destroy waitdemo
will@host:~$
will@host:~$ date
Thu Aug 18 22:44:54 NZST 2016
will@host:~$ sudo uvt-kvm create --cpu 8 --memory 2048 --disk 8 --ssh-public-key-file ~will/.ssh/authorized_keys waitdemo arch=amd64 release=vivid
will@host:~$ uvt-kvm wait --insecure waitdemo
Warning: Permanently added '192.168.122.3' (ECDSA) to the list of known hosts.

... no output ...

^CTraceback (most recent call last):
  File "/usr/bin/uvt-kvm", line 35, in <module>
    uvtool.libvirt.kvm.main_cli_wrapper(sys.argv[1:])
  File "/usr/lib/python2.7/dist-packages/uvtool/libvirt/kvm.py", line 709, in main_cli_wrapper
    main(*args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/uvtool/libvirt/kvm.py", line 704, in main
    args.func(parser, args)
  File "/usr/lib/python2.7/dist-packages/uvtool/libvirt/kvm.py", line 637, in main_wait
    main_wait_remote(parser, args)
  File "/usr/lib/python2.7/dist-packages/uvtool/libvirt/kvm.py", line 605, in main_wait_remote
    private_key_file=args.ssh_private_key_file,
  File "/usr/lib/python2.7/dist-packages/uvtool/libvirt/kvm.py", line 489, in ssh
    ssh_call, preexec_fn=subprocess_setup, close_fds=True, stdin=stdin
  File "/usr/lib/python2.7/subprocess.py", line 535, in check_call
    retcode = call(*popenargs, **kwargs)
  File "/usr/lib/python2.7/subprocess.py", line 522, in call
    return Popen(*popenargs, **kwargs).wait()
  File "/usr/lib/python2.7/subprocess.py", line 1376, in wait
    pid, sts = _eintr_retry_call(os.waitpid, self.pid, 0)
  File "/usr/lib/python2.7/subprocess.py", line 476, in _eintr_retry_call
    return func(*args)
KeyboardInterrupt