Document how to set a nameserver for the overcloud
Document how to set a nameserver for the overcloud

Change-Id: I767eab21f50fbfdd59643fc8acb5b6c8ff555ecb
Related: rhbz#1237214

dpkshetty/instack-undercloud,dpkshetty/instack-undercloud,eprasad/instack-undercloud,dmsimard/instack-undercloud,rdo-management/instack-undercloud,rdo-management/instack-undercloud,eprasad/instack-undercloud,dmsimard/instack-undercloud,bcrochet/instack-undercloud,bcrochet/instack-undercloud