confused domain argument for network create v2

[Guojian Shao]

The argument --domain of network create v2 is confused: http://docs.openstack.org/developer/python-openstackclient/command-objects/network.html#cmdoption-network-create--domain

we have used domain scope arguments --project-domain, --user-domain and --group-domain in identity commands, for example, role add v3, to prevent resources conflict from same resource name existence.

To keep with the style of identity commands, it's better to rename --domain to --project-domain.

[Steve Martinelli (stevemar)]

fixed at: https://review.openstack.org/195862