``openstack vnf graph set`` fails with no attribute error of 'param_file'

[Yoshito Ito]

When updating VNFFG with ``openstack vnf graph set' command, it fails with the attribute error.

The error message is:

Traceback (most recent call last):
  File "/usr/local/lib/python3.6/dist-packages/cliff/app.py", line 400, in run_subcommand
    result = cmd.run(parsed_args)
  File "/usr/local/lib/python3.6/dist-packages/osc_lib/command/command.py", line 41, in run
    return super(Command, self).run(parsed_args)
  File "/usr/local/lib/python3.6/dist-packages/cliff/display.py", line 117, in run
    column_names, data = self.take_action(parsed_args)
  File "/usr/local/lib/python3.6/dist-packages/tackerclient/osc/v1/nfvo/vnffg.py", line 305, in take_action
    vnffg = client.update_vnffg(obj_id, self.args2body(parsed_args))
  File "/usr/local/lib/python3.6/dist-packages/tackerclient/osc/v1/nfvo/vnffg.py", line 285, in args2body
    if parsed_args.param_file:
AttributeError: 'Namespace' object has no attribute 'param_file'
clean_up UpdateVNFFG: 'Namespace' object has no attribute 'param_file'
END return value: 1