test: Use beiboot on fedora-coreos

Our current fedora-coreos test setup overlays the bridge and the plugins
on the host and then additionally installs the various RPMs into a
container.  This is more or less what you needed to do in the
pre-beiboot world, but the container on its own has been sufficient for
quite some time.

Let's get rid of the "host" rpm-ostree install component and just use
the container straight-up, which is what we expect our users to be doing
anyway.

We keep the "podman container runlabel INSTALL" from the end of that
script as a separate `--run-command` in `image-prepare`: we still want
to test this stuff in privileged mode (vs. the rhel/ws-container
scenarios which test an unprivileged container).

Author: allisonkarlitskaya

test/image-prepare

@@ -155,7 +155,7 @@ def build_install_ostree(dist_tars: list[str], image: str, *, verbose: bool, qui
     args += [
         "--upload", os.path.join(BASE_DIR, "containers") + ":/var/tmp/",
         "--script", os.path.join(TEST_DIR, "ws-container.install"),
-        "--script", os.path.join(TEST_DIR, "ostree.install"),
+        "--run-command", "podman container runlabel INSTALL cockpit/ws",
         "--upload", os.path.join(BASE_DIR, "dist/playground") + ":/usr/local/share/cockpit/"]
     return args