Add go fuzzer in preparation for testing. Also gofmt a few files that needed it.

pkg/util/util_test.go

@@ -153,3 +153,11 @@ func TestIntOrStringMarshalJSON(t *testing.T) {
 		}
 	}
 }
+
+func TestStringDiff(t *testing.T) {
+	diff := StringDiff("aaabb", "aaacc")
+	expect := "aaa\n\nA: bb\n\nB: cc\n\n"
+	if diff != expect {
+		t.Errorf("diff returned %v", diff)
+	}
+}