vsphere/tags_helper.go
func (p *tagDiffProcessor) diffOldNew() []string {
	return p.diff(p.oldTagIDs, p.newTagIDs)
}
func (p *tagDiffProcessor) diffOldNew() []string {
	return p.diff(p.oldTagIDs, p.newTagIDs)
}
// diffOldNew returns any elements of old that were missing in new.