Adds Support for Configuring NTP Servers

Previously, the ntp servers used by an OpenShift deployment were
hard coded to:

['time.apple.com iburst', 'pool.ntp.org iburst', 'clock.redhat.com iburst']

This causes problems for deployments that do not allow ntp clock
synchronization with outside entities.  This patch adds the
$ntp_servers parameter for configuring an array of NTP servers and
uses the above mentioned array of servers to maintain backwards
compatibility.