downgrade log of util.ExecuteCommand (kubernetes-sigs#975)

As this error E0531 is not that ueful and no need to be mark
this as 'E', use Info level should be fine as this won't affect
return value.

(cherry picked from commit 97f25c9)

Author: jichenjc

pkg/util/util.go

@@ -161,13 +161,14 @@ func Copy(m *clusterv1.Machine) *clusterv1.Machine {
 }
 
 // ExecCommand Executes a local command in the current shell.
-func ExecCommand(name string, args ...string) string {
+func ExecCommand(name string, args ...string) (string, error) {
 	cmdOut, err := exec.Command(name, args...).Output()
 	if err != nil {
 		s := strings.Join(append([]string{name}, args...), " ")
-		klog.Errorf("error executing command %q: %v", s, err)
+		klog.Infof("Executing command %q: %v", s, err)
+		return string(""), err
 	}
-	return string(cmdOut)
+	return string(cmdOut), nil
 }
 
 // Filter filters a list for a string.