boot/grub: add rootwait to default config

It doesn't hurt, and is useful for removable boot media like a pendrive
that may depend on usb enumeration and isn't available immediately.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

boot/grub/menu.lst

@@ -13,4 +13,4 @@ background 	cccccc
 
 title Buildroot
 	root (hd0,0)
-	kernel /boot/bzImage rw root=/dev/sda1
+	kernel /boot/bzImage rw root=/dev/sda1 rootwait