[#255] services/audit: Skip all tasks from previous epoch in audit processor

Implement Reset method on audit task manager that cleans task queue.
Extended TaskManager interface with Reset method on IR side. Call Reset
method in audit processor before new audit start.

Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>

pkg/innerring/processors/audit/process.go

@@ -21,6 +21,7 @@ func (ap *Processor) processStartAudit(epoch uint64) {
 	log := ap.log.With(zap.Uint64("epoch", epoch))
 
 	ap.prevAuditCanceler()
+	ap.taskManager.Reset()
 
 	containers, err := ap.selectContainersToAudit(epoch)
 	if err != nil {

pkg/innerring/processors/audit/processor.go

@@ -30,6 +30,7 @@ type (
 
 	TaskManager interface {
 		PushTask(*audit.Task) error
+		Reset()
 	}
 
 	// Processor of events related with data audit.

pkg/services/audit/taskmanager/reset.go

@@ -0,0 +1,8 @@
+package audittask
+
+// Reset pops all tasks from the queue.
+func (m *Manager) Reset() {
+	for len(m.ch) > 0 {
+		<-m.ch
+	}
+}