NTP knobs..

[timothysc]

Need to setup sane defaults for NTP and have a knob'd override for large scale vendors.

[craigtracey]

We should ads ntp packages to the images, if not already present. Configuration should be handled by runtime config management.

[timothysc]

@detiber - history repeats itself ;-)

[detiber]

Currently ntp is installed on both Ubuntu and CentOS hosts. Since services are enabled by default when installing packages on Ubuntu the ntp service is already running with the default configuration. This isn't the case for CentOS, but since we only use Ubuntu for the Quickstart I am downgrading the priority.