Add note about /etc/hosts
Add note about /etc/hosts

Puppet doesn't work if the full hostname of the system is not
resolvable.

Change-Id: Ic8c8438fb7eba4b5c5ef8e120b8bb77c7de6a17a

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