Sorry, wrong repo - for python-neutronclient 2.2.0 there is insecure option, but it cannot be passed via cmdline or env variables.
root@ubuntu1210:/tmp/nv/python-neutronclient# grep 'insecure' -i -r ./
./quantumclient/client.py:                 endpoint_url=None, insecure=False,
./quantumclient/client.py:        self.disable_ssl_certificate_validation = insecure
./quantumclient/v2_0/client.py:    :param insecure: ssl certificate validation. (optional)