don't lose private data during destroy

Makre sure private data is maintained all the way to destroy. This
slipped through, since private data isn't used much for current
providers, except for timeouts.

terraform/eval_diff.go

@@ -448,8 +448,9 @@ func (n *EvalDiff) Eval(ctx EvalContext) (interface{}, error) {
 			// must _also_ record the returned change in the active plan,
 			// which the expression evaluator will use in preference to this
 			// incomplete value recorded in the state.
-			Status: states.ObjectPlanned,
-			Value:  plannedNewVal,
+			Status:  states.ObjectPlanned,
+			Value:   plannedNewVal,
+			Private: plannedPrivate,
 		}
 	}
 
@@ -790,6 +791,7 @@ func (n *EvalDiffDestroy) Eval(ctx EvalContext) (interface{}, error) {
 			Before: state.Value,
 			After:  cty.NullVal(cty.DynamicPseudoType),
 		},
+		Private:      state.Private,
 		ProviderAddr: n.ProviderAddr,
 	}