Add options for templated preseed

A recent patch to puppet-cobbler (9f96d21) removed a static
preseed file from the cobbler setup and replaced it with a
template.  This patch shows users how to add data for use
with the cobbler template.

Partial-Bug: #1263310
Switch cobbler to coi::profiles::cobbler_server

This change lets us use coi::profiles::cobbler_server instead
of the cobbler class, which makes it easier to hiera-ize data.
Move disk paritioning options to user.common.yaml

Since we're now using the cobbler_server profile from coi,
we should move this data accordingly.
Merge pull request #28 from CiscoSystems/bugs_1263310_

Add options for templated preseed