floatingip-create: fixed_ip_address and port_id not sent to server

The CreateFloatingIP command defines an args2body function for building the body of the request to the quantum server.
However, this method adds only the floating_network_id parameter.

This causes commands to be sent without some keyword parameters the command supports, namely --port-id and --fixed-ip-address

The workaround is to use the command in the following way:

quantum floatingip-create <floating_network_id> -- --fixed_ip_address <address> --port_id <port_id> (note the underscores in the parameters names)