CA-1046764: GenID should only be set for Win8/Win12
CA-1046764: GenID should only be set for Win8/Win12

This patch was missed prior to the CP-4204 merge. We now have an optional
parameter to set the generation id for HVM templates.

Signed-off-by: Mike McClurg <d5d39725aee3103039228164deec3c7acc6f60e3@citrix.com>

xenserver/guest-templates,xenserver/guest-templates