Data mappings for preseed package selection

Add data mappings and variables for selecting additional packages to be
installed by the Cobbler preseed.

Change-Id: If7341b00d4ebb9aef82eb003ecc8bf342f6c2d5d
Closes-Bug: #1317195
Merge pull request #91 from CiscoSystems/bugs/1317195

Data mappings for preseed package selection