CA-207565: Update `is_vmss_snapshot` field for VSS snapshot
CA-207565: Update `is_vmss_snapshot` field for VSS snapshot

For VSS snapshot taken from VMSS policy `is_vmss_snapshot` field
must be set to True.

Signed-off-by: Sharad Yadav <0ab5d8dd51ae0f2f9ed283cbbbb7a94d110e3347@citrix.com>

Frezzle/xen-api,euanh/xen-api,Frezzle/xen-api,srowe/xen-api,Frezzle/xen-api,Frezzle/xen-api,euanh/xen-api,euanh/xen-api,Frezzle/xen-api,srowe/xen-api,euanh/xen-api,euanh/xen-api,euanh/xen-api,srowe/xen-api,srowe/xen-api,srowe/xen-api