leapp preupgrade failed to select the BaseOS and Appstream repositories

Issue

• The leapp preupgrade command failed with the following error.

==> Processing phase `TargetTransactionFactsCollection`
====> * target_userspace_creator
        Initializes a directory to be populated as a minimal environment to run binaries from the target system.
Red Hat CodeReady Linux Builder for RHEL 8 x86_  12 MB/s | 5.7 MB     00:00

<... snip ...>

Traceback (most recent call last):
  File "/usr/lib64/python2.7/multiprocessing/process.py", line 258, in _bootstrap
    self.run()
  File "/usr/lib64/python2.7/multiprocessing/process.py", line 114, in run
    self._target(*self._args, **self._kwargs)
  File "/usr/lib/python2.7/site-packages/leapp/repository/actor_definition.py", line 72, in _do_run
    actor_instance.run(*args, **kwargs)
  File "/usr/lib/python2.7/site-packages/leapp/actors/__init__.py", line 335, in run
    self.process(*args)
  File "/usr/share/leapp-repository/repositories/system_upgrade/common/actors/targetuserspacecreator/actor.py", line 52, in process
    userspacegen.perform()
  File "/usr/lib/python2.7/site-packages/leapp/utils/deprecation.py", line 42, in process_wrapper
    return target_item(*args, **kwargs)
  File "/usr/share/leapp-repository/repositories/system_upgrade/common/actors/targetuserspacecreator/libraries/userspacegen.py", line 681, in perform
    _create_target_userspace(context, indata.packages, indata.files, target_repoids)
  File "/usr/share/leapp-repository/repositories/system_upgrade/common/actors/targetuserspacecreator/libraries/userspacegen.py", line 655, in _create_target_userspace
    _prep_repository_access(context, target_path)
  File "/usr/share/leapp-repository/repositories/system_upgrade/common/actors/targetuserspacecreator/libraries/userspacegen.py", line 246, in _prep_repository_access
    files_owned_by_rpms = _get_files_owned_by_rpms(target_context, '/etc/yum.repos.d')
  File "/usr/share/leapp-repository/repositories/system_upgrade/common/actors/targetuserspacecreator/libraries/userspacegen.py", line 214, in _get_files_owned_by_rpms
    for fname in os.listdir(context.full_path(dirpath)):
OSError: [Errno 2] No such file or directory: '/var/lib/leapp/el8userspace/etc/yum.repos.d'

• The following is the executed command in /var/log/leapp/leapp-preupgrade.log. The CodeReady repository only was used clearly. The BaseOS and AppStream repositries were not selected.

DEBUG    PID: XXXXX leapp.workflow.TargetTransactionFactsCollection.target_userspace_creator: External command has started: ['systemd-nspawn', '--register=no', '--quiet', '-D', '/var/lib/leapp/scratch/mounts/root_/system_overlay', <... snip ...> 'dnf', 'install', '-y', '--nogpgcheck', '--setopt=module_platform_id=platform:el8', '--setopt=keepcache=1', '--releasever', u'8.4', '--installroot', '/el8target', '--disablerepo', '*', '--enablerepo', u'codeready-builder-for-rhel-8-x86_64-rpms', 'dnf', 'dnf-command(config-manager)']