We should be managing the network configuration with os-net-config or
elsewhere so we should not be providing a nameserver in resolv.conf
in overcloud images. This element will be used to ensure that the
resolv.conf of the overcloud-full image should not contain any
nameservers.
Change-Id: If8c44137d120059b356675a074e3af23ea63a6f8
Partial-Bug: #1749756