vsphere/nas_datastore_helper.go
func (p *nasDatastoreMountProcessor) diffNewOld() []string {
	return p.diff(p.newHSIDs, p.oldHSIDs)
}
func (p *nasDatastoreMountProcessor) diffNewOld() []string {
	return p.diff(p.newHSIDs, p.oldHSIDs)
}
// diffNewOld returns any elements of new that were missing in old.