CA-104674: Don't add genid to VMs that don't need one

VM.clone was erroneously adding a fresh generation ID to template VMs which
weren't set with "O:O". We now check for blank generation IDs and preserve
them.

Signed-off-by: Mike McClurg <mike.mcclurg@citrix.com>
Merge pull request #1320 from mcclurmc/ca104674-genid-master

CA-104674: Don't add genid to VMs that don't need one