rpmostree-core: Reload user/groups after each %post script

As part of the migration to direct sysusers support in RPMs, packages
are no longer creating their users/groups in %pre scripts as they rely
on RPM to do the work.

In rpm-ostree unified core composes, the users/groups are not created
this way as we don't use/call out to those new RPM scriptlets.

Thus the "new" users (i.e. those not part of the default `passwd` &
`group` files set in the manifests) are created when the systemd %post
scriptlet runs the `sysusers` command.

As a workaround, we now reload the list of users/groups after each %post
to make sure it is up-to-date.

See: https://fedoraproject.org/wiki/Changes/RPMSuportForSystemdSysusers
See: rpm-software-management/rpm@009d139

See: fedora-silverblue/issue-tracker#636
See: https://gitlab.com/fedora/ostree/sig/-/issues/70
See: #5333

Author: travier

src/libpriv/rpmostree-core.cxx

@@ -4518,23 +4518,23 @@ rpmostree_context_assemble (RpmOstreeContext *self, GCancellable *cancellable, G
             return FALSE;
         }
 
-      if (faccessat (tmprootfs_dfd, "etc/passwd", F_OK, 0) == 0)
-        {
-          CXX_TRY (passwd_entries->add_passwd_content (tmprootfs_dfd, "etc/passwd"), error);
-        }
-
-      if (faccessat (tmprootfs_dfd, "etc/group", F_OK, 0) == 0)
-        {
-          CXX_TRY (passwd_entries->add_group_content (tmprootfs_dfd, "etc/group"), error);
-        }
-
       {
         auto task = rpmostreecxx::progress_begin_task ("Running post scripts");
         guint n_post_scripts_run = 0;
 
         /* %post */
         for (guint i = 0; i < n_rpmts_elements; i++)
           {
+            if (faccessat (tmprootfs_dfd, "etc/passwd", F_OK, 0) == 0)
+              {
+                CXX_TRY (passwd_entries->add_passwd_content (tmprootfs_dfd, "etc/passwd"), error);
+              }
+
+            if (faccessat (tmprootfs_dfd, "etc/group", F_OK, 0) == 0)
+              {
+                CXX_TRY (passwd_entries->add_group_content (tmprootfs_dfd, "etc/group"), error);
+              }
+
             rpmte te = rpmtsElement (ordering_ts, i);
             if (rpmteType (te) != TR_ADDED)
               continue;