Missing str() cast in args to Popen

[Walter Doekes]

BT for zfs destination move.

Traceback (most recent call last):
  File "/usr/local/bin/proxmove", line 1591, in <module>
    main()
  File "/usr/local/bin/proxmove", line 1587, in main
    vmmover.run(options.dry_run)
  File "/usr/local/bin/proxmove", line 1310, in run
    self.move_vm(vm, translator, dry_run)
  File "/usr/local/bin/proxmove", line 1397, in move_vm
    dst_vm.create_volume(key, volume, storage=storage)
  File "/usr/local/bin/proxmove", line 976, in create_volume
    new_volume = source_volume.clone(storage, self.id, key)
  File "/usr/local/bin/proxmove", line 1152, in clone
    new_storage, new_vmid, new_name)
  File "/usr/local/bin/proxmove", line 509, in copy
    disk_size, dst_temp, src_format, dst_id, dst_name)
  File "/usr/local/bin/proxmove", line 795, in copy_from_temp
    self.ssh_command(['zfs', 'create', '-V', disk_size, dst_zfs])
  File "/usr/local/bin/proxmove", line 568, in ssh_command
    self.ssh] + extra + command, hide_stderr=hide_stderr, tty=tty)
  File "/usr/local/bin/proxmove", line 547, in run_command
    return subprocess.check_output(command, **kwargs)
  File "/usr/lib/python3.5/subprocess.py", line 626, in check_output
    **kwargs).stdout
  File "/usr/lib/python3.5/subprocess.py", line 693, in run
    with Popen(*popenargs, **kwargs) as process:
  File "/usr/lib/python3.5/subprocess.py", line 947, in __init__
    restore_signals, start_new_session)
  File "/usr/lib/python3.5/subprocess.py", line 1490, in _execute_child
    restore_signals, start_new_session, preexec_fn)
TypeError: Can't convert 'int' object to str implicitly