Remove empty metadata_settings from iscsid and multipathd templates
metadata_settings is meant to have a specific format or be completely
absent. Unfortunately the hook [1] doesn't an empty value for this. So
we remove it as an easy fix before figuring out how to add such a
functionality to the hook.
[1] https://github.com/openstack/tripleo-heat-templates/blob/master/extraconfig/nova_metadata/krb-service-principals.yaml
Co-Authored-By: Thomas Herve <therve@redhat.com>
Change-Id: Ieac62a8076e421b5c4843a3cbe1c8fa9e3825b38