osbuild: run further setup in build environment

Introduce `run-stage` script, which sets up the build environment before
running the stage. Run `ldconfig`, `systemd-sysusers`, and
`systemd-tmpfiles` in it.

osbuild

@@ -81,9 +81,10 @@ def main(pipeline_path, from_archive, save):
                                 f"--directory={root}",
                                 f"--bind={tree}:/tmp/tree",
                                 f"--bind={os.getcwd()}/state/{name}:/tmp/state",
+                                f"--bind={os.getcwd()}/run-stage:/tmp/run-stage",
                                 f"--bind={os.getcwd()}/stages/{name}:/tmp/stage",
                                 "--bind=/etc/pki",
-                                "/tmp/stage"],
+                                "/tmp/run-stage", "/tmp/stage"],
                     input=options_str, encoding="utf-8", check=True)
             except KeyboardInterrupt:
                 print()

run-stage

@@ -0,0 +1,24 @@
+#!/usr/bin/python3
+
+import argparse
+import subprocess
+import sys
+
+
+def main(stage):
+    subprocess.run(["ldconfig"], check=True)
+    subprocess.run(["systemd-sysusers"], check=True)
+
+    # Allow systemd-tmpfiles to return non-0. Some packages want to create
+    # directories owned by users that are not set up with systemd-sysusers.
+    subprocess.run(["systemd-tmpfiles", "--create"])
+
+    r = subprocess.run([stage])
+    return r.returncode
+
+
+if __name__ == "__main__":
+    parser = argparse.ArgumentParser()
+    parser.add_argument("stage")
+    args = parser.parse_args()
+    sys.exit(main(**vars(args)))

stages/io.weldr.anaconda

@@ -88,13 +88,6 @@ def main(tree, state, kickstart, skip_package_install=False):
     with open("/etc/anaconda/product.d/fedora.conf", "w") as f:
         f.write(product)
 
-    subprocess.run(["ldconfig"], check=True)
-    subprocess.run(["systemd-sysusers"], check=True)
-
-    # Allow systemd-tmpfiles to return non-0. Some packages want to create
-    # directories owned by users that are not set up with systemd-sysusers.
-    subprocess.run(["systemd-tmpfiles", "--create"])
-
     cmd = [
         "anaconda",
         "--cmdline",