Add ability to distinguish between user defined and system defined guest OS and mappings
Add default mappings for XenServer
Local testing with
1. Add new guest OS by API
2. Add new guest OS mapping by API
Add APIs for ability to add new guest OS types, and their hypervisor specific mappings.
The table guest_os_hypervisor is currently maintained but not used, and the APIs reuse the same
Signed off by: Nitin Mehta <nitin.mehta@citrix.com>