Do not set domain parameters for V2 auth

[Dmitry Tantsur]

Currently we allow to use keystone V2, but we always set user_domain_name and project_domain_name. This happened to work for some time, but now it causes a failure in keystoneauth: https://github.com/openstack/keystoneauth/blob/71faf95b97f96ffb0a550501c824def10b16ec70/keystoneauth1/identity/generic/base.py#L149-L152. Instead of this, we should set default_domain_name and leave these two unset. The default_domain_name option seems ignored when V2 is used.

Example of a failure: http://logs.openstack.org/22/535622/7/check/puppet-openstack-beaker-centos-7/d04885d/logs/ironic-inspector/ironic-inspector.txt.gz#_2018-01-30_09_04_43_152