CLOS-4056 follow-up: target_userspace_creator: tolerate missing dnf-plugin-spacewalk config

When the target userspace is built from no-auth-aware repos
(rhn-client-tools >= 3.0.1, which Obsoletes dnf-plugin-spacewalk on CL8/9
per CLOS-4056), /etc/dnf/plugins/spacewalk.conf is absent in
/var/lib/leapp/elNuserspace/. The unconditional `open(spacewalk_conf, 'r')`
inside `if os.path.isdir('/etc/sysconfig/rhn')` then raises

    IOError: [Errno 2] No such file or directory: '/var/lib/leapp/el8userspace/etc/dnf/plugins/spacewalk.conf'

and target_userspace_creator crashes with exit code 1, blocking preupgrade
on every CL7+CLN -> CL8+no_auth transition where the new RC packages reach
the target.

Surfaced during CLOS-4056 verification (elevate-qa Run #3 build #40 with
BS_BUILDS_TARGET delivery wired up correctly via leapp_upgrade_repositories.repo
late-append). The outer /etc/sysconfig/rhn check is correct (CLN registration
may persist on no-auth for licensing), but the inner file presence is no
longer guaranteed - guard it with an explicit os.path.isfile check.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: prilr

repos/system_upgrade/common/actors/targetuserspacecreator/libraries/userspacegen.py

@@ -681,16 +681,26 @@ def _prep_repository_access(context, target_userspace):
         run(['rm', '-rf', os.path.join(target_etc, 'rhsm')])
         context.copytree_from('/etc/rhsm', os.path.join(target_etc, 'rhsm'))
 
-    if os.path.isdir('/etc/sysconfig/rhn'):
+    # Set up spacewalk plugin config in the target chroot only if the plugin's
+    # config file actually exists there. Under the no-auth migration (CLOS-4056)
+    # rhn-client-tools >= 3.0.1 Obsoletes dnf-plugin-spacewalk on CL8/9, so
+    # the target userspace built from the no-auth-aware repos has no
+    # /etc/dnf/plugins/spacewalk.conf - the original unconditional open
+    # raised IOError [Errno 2] and crashed target_userspace_creator. The
+    # outer /etc/sysconfig/rhn directory check is on the source side and
+    # remains valid (CLN registration may persist for licensing/inventory),
+    # but the inner file presence is no longer guaranteed.
+    spacewalk_conf = os.path.join(target_etc, 'dnf/plugins/spacewalk.conf')
+    if os.path.isdir('/etc/sysconfig/rhn') and os.path.isfile(spacewalk_conf):
         # Set up spacewalk plugin config
-        with open(os.path.join(target_etc, 'dnf/plugins/spacewalk.conf'), 'r') as f:
+        with open(spacewalk_conf, 'r') as f:
             lines = f.readlines()
             new_lines = []
             for line in lines:
                 if 'enabled' in line:
                     line = 'enabled = 1\n'
                 new_lines.append(line)
-        with open(os.path.join(target_etc, 'dnf/plugins/spacewalk.conf'), 'w') as f:
+        with open(spacewalk_conf, 'w') as f:
             f.writelines(new_lines)
 
     if os.path.isfile('/etc/mirrorlist'):