Add "firmware" as an option for the hardware section, allowing values of
"efi" or "bios" (default "bios") so that the firmware is defined at the
machine create stage.
* Add new config option to allow setting virtual machine hardware version
The vsphere-iso builder gets a new configuration option named
vm_version. It allows setting the VMWare virtual machine hardware
version to a non-default value.
The default behavior remains unchanged. Use the latest supported
hardware version that ESXi/vCenter allows.
VMWare KB for supported virtual machine hardware versions.
https://kb.vmware.com/s/article/1003746
* Change vm_version from string to int
Michael Kuzmin
John O'Connor
Vladislav Rassokhin
Sean Malloy
Andrei Tonkikh