Auto-enable 4k sector alignment when disk encryption is requested (it is

required in such a case). But don't prevent the user from pointing the
gun at his/her foot -- you can disable 4k alignment after enabling geli).

MFC after:	3 days

usr.sbin/bsdinstall/scripts/zfsboot

@@ -1372,6 +1372,7 @@ while :; do
 		if [ "$ZFSBOOT_GELI_ENCRYPTION" ]; then
 			ZFSBOOT_GELI_ENCRYPTION=
 		else
+			ZFSBOOT_GNOP_4K_FORCE_ALIGN=1
 			ZFSBOOT_GELI_ENCRYPTION=1
 		fi
 		;;