not set verify flag when creating token-session

[chenyujie]

When keystone endpoint is based on self-signed https, get_network_driver would be failed because of SSL problem.

Relative code abstract as following:

    def get_network_driver(context):
...
        session = auth_utils.get_token_client_session(
            context.auth_token, context.tenant)
...
def get_token_client_session(token=None, project_id=None, conf=None):
...
    session = ks_session.Session(auth=token_auth)
    _set_ssl_parameters(conf, session)
...
def _set_ssl_parameters(conf_section, session):
    if not conf_section:
        return

The fix should be:
def _set_ssl_parameters(conf_section, session):
    if not conf_section:
        conf_section = cfg.CONF.keystone_authtoken