installer: Exclude systemd-container

This is a new package that may show up, let's just hardcode excluding
it for now.  It definitely won't work in an installer environment.
imagefactory: Output compat=0.10 qcow2 by default

So it can be read by RHEL6 era qemu.  Anyone who wants to take
advantage of the later format version can convert it when importing
into their infrastructure.