Make sure the build under test installs smoothly including the
multilib subpackages needed for the CI tests. Use a setup task
prepare.sh to accomplish that.
The "standard" CI installer installs whole the x86_64 build
minus glibc-headers-s390, which is a noarch package having
file conflicts with glibc-headers-x86 (which is another
noarch subrpm). The prepare.sh then installs needed i686
packages.
