Adds NOZEROCONF option to CentOS Image Guide

The "NOZEROCONF=yes" option is a requirement for successful
access to the metadata service. By default in RHEL (or derivatives)
this option is not present.

Change-Id: Ic9427fd17ad08955d7a5a9e4c2f1227260999701
Closes-Bug: #1273916
backport: havana
Merge "Adds NOZEROCONF option to CentOS Image Guide"