Make LazyMultiError only constructable via function

common/errors/multierror_test.go

Index: common/errors/multierror_test.go
diff --git a/common/errors/multierror_test.go b/common/errors/multierror_test.go
index a7a15329e1f430accde5798033af90a1a3d0b129..435cc452c9982f916c92494969ecbc9b5eed0974 100644
--- a/common/errors/multierror_test.go
+++ b/common/errors/multierror_test.go
@@ -65,7 +65,7 @@ func TestLazyMultiError(t *testing.T) {
 	t.Parallel()
 
 	Convey("Test LazyMultiError", t, func() {
-		lme := LazyMultiError{Size: 10}
+		lme := NewLazyMultiError(10)
 		So(lme.Get(), ShouldEqual, nil)
 
 		e := errors.New("sup")
@@ -80,7 +80,7 @@ func TestLazyMultiError(t *testing.T) {
 		So(func() { lme.Assign(20, e) }, ShouldPanic)
 
 		Convey("Try to freak out the race detector", func() {
-			lme := LazyMultiError{Size: 64}
+			lme := NewLazyMultiError(64)
 			Convey("all nils", func() {
 				wg := sync.WaitGroup{}
 				for i := 0; i < 64; i++ {