dwke: use makedirs() to create output directory

to support hierarchical sections (e.g. sid/main)

Signed-off-by: Andreas Beckmann <anbe@debian.org>
p: fix bad indent

Signed-off-by: Andreas Beckmann <anbe@debian.org>
p: add --arch option to support testing a non-default architecture

e.g. allows testing i386 on an amd64 host
(without requiring the slave to run in an i386 chroot)

Signed-off-by: Andreas Beckmann <anbe@debian.org>