test: Avoid repository update in fedora-coreos preparation
test: Avoid repository update in fedora-coreos preparation

We don't want/expect rpm-ostree to change anything else than the
explicitly given RPMs. So there is no need to update the package index
or upgrade any dependency. This makes the VM preparation faster and more
reliable.

mvollmer/cockpit,martinpitt/cockpit,martinpitt/cockpit,cockpit-project/cockpit,mvollmer/cockpit,martinpitt/cockpit,cockpit-project/cockpit,mvollmer/cockpit,cockpit-project/cockpit,cockpit-project/cockpit,mvollmer/cockpit,mvollmer/cockpit,cockpit-project/cockpit,martinpitt/cockpit,martinpitt/cockpit