Add support for specifying the primary virtual disk format when creating VM on a datastore cluster

[devblackops]

Currently, when creating a new VM, it is not possible to specify the disk format when the VM is created on a datastore cluster (SDRS). Instead, the disk will inherit the format from the template it is based on.

This is a limitation with PowerCLI's New-VM cmdlet where you cannot specify the 'DiskStorageFormat' parameter when creating a VM on a datastore cluster.