Image generations is currently failing on builbots due to the following
errors:
mkfwimage -B XS2 -v XS2 [...] ath25-ubnt2-squashfs-sysupgrade.bin
ERROR: Failed creating firmware layout description - error code: -2
mkfwimage -B XS5 -v XS5 [...] ath25-ubnt5-squashfs-sysupgrade.bin
ERROR: Failed creating firmware layout description - error code: -2
That cryptic -2 error simply means, that kernel+rootfs doesn't fit into
the firmware partition.
Signed-off-by: Petr Štetiar <ynezz@true.cz>