Remove environment defaults
Remove environment defaults

neutronclient uses os-client-config behind the scenes, which provides
default values from the environment as well for all of these values.
However, occ does it in a way that does allows incorporating config
file based options as well. Setting env var defaults to argparse here
winds up with two different systems fighting for variable precedence.

Change-Id: I4dc95a72873391530d224add8095d7bbe8c445b8

openstack/python-neutronclient,Juniper/python-neutronclient,huntxu/python-neutronclient,noironetworks/python-neutronclient,openstack/python-neutronclient,Juniper/python-neutronclient,noironetworks/python-neutronclient,huntxu/python-neutronclient