daemon/ProcessEvent: make sure to cancel the contexts

Reported by govet linter:

> daemon/monitor.go:57:9: lostcancel: the cancel function returned by context.WithTimeout should be called, not discarded, to avoid a context leak (govet)
> 			ctx, _ := context.WithTimeout(context.Background(), 2*time.Second)
> 			     ^
> daemon/monitor.go:128:9: lostcancel: the cancel function returned by context.WithTimeout should be called, not discarded, to avoid a context leak (govet)
> 			ctx, _ := context.WithTimeout(context.Background(), 2*time.Second)
> 			     ^

Fixes: b5f288 ("Handle blocked I/O of exec'd processes")
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

daemon/monitor.go

@@ -54,9 +54,9 @@ func (daemon *Daemon) ProcessEvent(id string, e libcontainerdtypes.EventType, ei
 			if err != nil {
 				logrus.WithError(err).Warnf("failed to delete container %s from containerd", c.ID)
 			}
-			ctx, _ := context.WithTimeout(context.Background(), 2*time.Second)
-
+			ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
 			c.StreamConfig.Wait(ctx)
+			cancel()
 			c.Reset(false)
 
 			exitStatus := container.ExitStatus{
@@ -125,8 +125,9 @@ func (daemon *Daemon) ProcessEvent(id string, e libcontainerdtypes.EventType, ei
 			execConfig.ExitCode = &ec
 			execConfig.Running = false
 
-			ctx, _ := context.WithTimeout(context.Background(), 2*time.Second)
+			ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
 			execConfig.StreamConfig.Wait(ctx)
+			cancel()
 
 			if err := execConfig.CloseStreams(); err != nil {
 				logrus.Errorf("failed to cleanup exec %s streams: %s", c.ID, err)