utils/genrandconfig: test per-package directories

Now that the support for per-package directories has been merged, it
is time to get some exposure for it in the autobuilders, so let's
build 1 out of 15 builds with this feature enabled, at least as an
initial step.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>