Add metrics for envelop transformer:

transformation_operation_count
    transformation_failures_count
    envelope_transformation_cache_misses_count
    data_key_generation_latencies_microseconds
    data_key_generation_failures_count

test/integration/master/kms_transformation_test.go

@@ -144,6 +144,7 @@ func TestKMSProvider(t *testing.T) {
 	if secretVal != string(s.Data[secretKey]) {
 		t.Fatalf("expected %s from KubeAPI, but got %s", secretVal, string(s.Data[secretKey]))
 	}
+	test.printMetrics()
 }
 
 func getDEKFromKMSPlugin(pluginMock *base64Plugin) ([]byte, error) {