Fix deadlock when task's exec start fails

Signed-off-by: Kenfe-Mickael Laventure <mickael.laventure@gmail.com>

io.go

@@ -1,6 +1,7 @@
 package containerd
 
 import (
+	"context"
 	"fmt"
 	"io"
 	"io/ioutil"
@@ -18,6 +19,13 @@ type IO struct {
 	closer *wgCloser
 }
 
+func (i *IO) Cancel() {
+	if i.closer == nil {
+		return
+	}
+	i.closer.Cancel()
+}
+
 func (i *IO) Wait() {
 	if i.closer == nil {
 		return
@@ -134,9 +142,10 @@ type ioSet struct {
 }
 
 type wgCloser struct {
-	wg  *sync.WaitGroup
-	dir string
-	set []io.Closer
+	wg     *sync.WaitGroup
+	dir    string
+	set    []io.Closer
+	cancel context.CancelFunc
 }
 
 func (g *wgCloser) Wait() {
@@ -152,3 +161,7 @@ func (g *wgCloser) Close() error {
 	}
 	return nil
 }
+
+func (g *wgCloser) Cancel() {
+	g.cancel()
+}