Remove ntp data from system plug-in

Ntp information belongs in the ntp plug-in.. Duh. Move the few
files collected in the system module to ntp.py.

Signed-off-by: Bryn M. Reeves <bmr@redhat.com>
Remove duplicate code in system plug-in

The Red Hat and Debian/Ubuntu system plug-ins are identical. Get
rid of them and have a comon System class.

Signed-off-by: Bryn M. Reeves <bmr@redhat.com>