patchtest has a layer (meta-patchtest) which contains relevant metadata for creating a image (guest). The intention with this machine is that it can be automatically launched (by a cronjob), execute patchtest and power down. The latter step is hanging.
Fixed by http://git.yoctoproject.org/cgit/cgit.cgi/patchtest/commit/?id=612403a9965b99c3064e167b91effc3c875ff717