support disk_controller for vapp disk

[zyxep]

Hi,

Looking at https://github.com/vmware/pyvcloud/blob/master/pyvcloud/vcd/vapp.py#L662 then there is support for disk_controller, it defaults to lsilogic.

Looking at the code https://github.com/vmware/vcd-cli/blob/623a322b61773a586cd5632ded0869a27b3e6d03/vcd_cli/vapp.py#L1072-L1096 isn't it used, not even as an option.

task = vapp.add_disk_to_vm(vm_name, size)
It would be nice to have support to be able to change the controller for new disks, I don't want to use lsilogic but Paravirtual