Fix go vet errors

Author: xia0pin9

client.go

@@ -607,7 +607,7 @@ func (c *UncachedHTTPClient) getHTTPDataWithContext(ctx context.Context, method
 					// If the failure is non authentication related, retry if we got a 500.
 					if (resp.Code != InternalServerErrorCode) || (i == maxRetryAttempts) {
 						// If we get a 500, we need to retry the request.
-						return fmt.Errorf(resp.Message)
+						return fmt.Errorf("%s", resp.Message)
 					}
 
 					// Check context before sleeping

client/tink_keyset_helper_test.go

@@ -231,7 +231,7 @@ func TestGetTinkKeysetHandleFromKnoxVersionList(t *testing.T) {
 	dummyVersionList, tinkKeyIDtoKnoxVersionID := getDummyKnoxVersionList(1000, keyTemplate)
 	keysetHandle, mapping, err := getTinkKeysetHandleFromKnoxVersionList(dummyVersionList)
 	if err != nil {
-		t.Fatalf(err.Error())
+		t.Fatalf("%s", err.Error())
 	}
 	if _, err := aead.New(keysetHandle); err != nil {
 		t.Fatalf("cannot get primitive from generated keyset handle: %s", err)
@@ -284,7 +284,7 @@ func TestGetKeysetInfoFromTinkKeysetHandle(t *testing.T) {
 	}
 	keysetInfoForPrint, err := json.MarshalIndent(keysetInfo, "", "  ")
 	if err != nil {
-		t.Fatalf(err.Error())
+		t.Fatalf("%s", err.Error())
 	}
 	expected := string(keysetInfoForPrint)
 	got, err := getKeysetInfoFromTinkKeysetHandle(keysetHandle, tinkKeyIDToKnoxVersionID)