EC2: Tell gptboot to skip its 3 second wait

Nobody is going to hit a key to tell gptboot to select another disk,
so there's no point waiting.

release/tools/ec2.conf

@@ -88,6 +88,10 @@ EOF
 	echo 'autoboot_delay="-1"' >> ${DESTDIR}/boot/loader.conf
 	echo 'beastie_disable="YES"' >> ${DESTDIR}/boot/loader.conf
 
+	# Tell gptboot not to wait 3 seconds for a keypress which won't
+	# arrive either.
+	printf -- "-n\n" > ${DESTDIR}/boot.config
+
 	# The emulated keyboard attached to EC2 instances is inaccessible to
 	# users, and there is no mouse attached at all; disable to keyboard
 	# and the keyboard controller (to which the mouse would attach, if