[#255] ir/audit: Make task manager to return number of skipped tasks

Add numeric return from TaskManager.Reset method that shows the number of
canceled tasks. This values will be used for assessment of the progress of
the audit.

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

pkg/innerring/processors/audit/process.go

@@ -21,7 +21,13 @@ func (ap *Processor) processStartAudit(epoch uint64) {
 	log := ap.log.With(zap.Uint64("epoch", epoch))
 
 	ap.prevAuditCanceler()
-	ap.taskManager.Reset()
+
+	skipped := ap.taskManager.Reset()
+	if skipped > 0 {
+		ap.log.Info("some tasks from previous epoch are skipped",
+			zap.Int("amount", skipped),
+		)
+	}
 
 	containers, err := ap.selectContainersToAudit(epoch)
 	if err != nil {