refactored mount, attach, resize operation's so that all failures generate events and event generation is more consistent.

refactored operation generator and operation executor to use more general generated functions for operations, completions, and events.

pkg/volume/util/metrics.go

@@ -49,12 +49,12 @@ func registerMetrics() {
 }
 
 // OperationCompleteHook returns a hook to call when an operation is completed
-func OperationCompleteHook(plugin, operationName string) func(error) {
+func OperationCompleteHook(plugin, operationName string) func(*error) {
 	requestTime := time.Now()
-	opComplete := func(err error) {
+	opComplete := func(err *error) {
 		timeTaken := time.Since(requestTime).Seconds()
 		// Create metric with operation name and plugin name
-		if err != nil {
+		if *err != nil {
 			storageOperationErrorMetric.WithLabelValues(plugin, operationName).Inc()
 		} else {
 			storageOperationMetric.WithLabelValues(plugin, operationName).Observe(timeTaken)