fix TestExitCode

Docker-DCO-1.1-Signed-off-by: Victor Vieux <victor.vieux@docker.com> (github: vieux)
Upstream-commit: 720f64af1855235b6f518ad97dbb89eb61191222
Component: engine

components/engine/execdriver/lxc/driver.go

@@ -155,7 +155,9 @@ func (d *driver) Run(c *execdriver.Command, startCallback execdriver.StartCallba
 	)
 	go func() {
 		if err := c.Wait(); err != nil {
-			waitErr = err
+			if _, ok := err.(*exec.ExitError); !ok { // Do not propagate the error if it's simply a status code != 0
+				waitErr = err
+			}
 		}
 		close(waitLock)
 	}()