Fix proposed /etc/ntp.conf

The sample /etc/ntp.conf file as provided at <http://docs.openstack.org/trunk/openstack-compute/install/apt/content/osfolubuntu-prerquisite.html> had some confusing or inaccurate information, as well as some incorrect configuration settings.  Updated to be more in line with correct settings and current recommendations from <http://support.ntp.org/bin/view/Support/WebHome>.

Change-Id: I624b805a3cb3663fa985c90b48273e0f84494212
Merge "Fix proposed /etc/ntp.conf"