Propagate context to exec delete

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>
(cherry picked from commit 96e0ba1afb228b48aa6e08a90cfc665083d24ccc)
Signed-off-by: Andrew Hsu <andrewhsu@docker.com>

libcontainerd/client_daemon.go

@@ -384,7 +384,7 @@ func (c *client) Exec(ctx context.Context, containerID, processID string, spec *
 	defer close(stdinCloseSync)
 
 	if err = p.Start(ctx); err != nil {
-		p.Delete(context.Background())
+		p.Delete(ctx)
 		ctr.deleteProcess(processID)
 		return -1, wrapError(err)
 	}