leapp preupgrade fails with "OS Error [error no 28] no space left on device"

Issue

• leapp preupgrade from RHEL 7 to RHEL 8 fails with :

  Traceback (most recent call last):
  File "/bin/leapp", line 9, in <module>
    load_entry_point('leapp==0.17.0', 'console_scripts', 'leapp')()
  File "/usr/lib/python2.7/site-packages/leapp/cli/__init__.py", line 45, in main
    cli.command.execute('leapp version {}'.format(VERSION))
  File "/usr/lib/python2.7/site-packages/leapp/utils/clicmd.py", line 111, in execute
    args.func(args)
  File "/usr/lib/python2.7/site-packages/leapp/utils/clicmd.py", line 133, in called
    self.target(args)
  File "/usr/lib/python2.7/site-packages/leapp/cli/commands/upgrade/breadcrumbs.py", line 166, in wrapper
    return f(*args, breadcrumbs=breadcrumbs, **kwargs)
  File "/usr/lib/python2.7/site-packages/leapp/cli/commands/preupgrade/__init__.py", line 58, in preupgrade
    repositories = util.load_repositories()
  File "/usr/lib/python2.7/site-packages/leapp/cli/commands/upgrade/util.py", line 90, in load_repositories
    manager.load()
  File "/usr/lib/python2.7/site-packages/leapp/repository/manager.py", line 120, in load
    repo.load(resolve=False, stage=_LoadStage.ACTORS, skip_actors_discovery=skip_actors_discovery)
  File "/usr/lib/python2.7/site-packages/leapp/repository/__init__.py", line 153, in load
    actor.discover()
  File "/usr/lib/python2.7/site-packages/leapp/repository/actor_definition.py", line 207, in discover
    q = Queue(1)
  File "/usr/lib64/python2.7/multiprocessing/__init__.py", line 218, in Queue
    return Queue(maxsize)
  File "/usr/lib64/python2.7/multiprocessing/queues.py", line 69, in __init__
    self._sem = BoundedSemaphore(maxsize)
  File "/usr/lib64/python2.7/multiprocessing/synchronize.py", line 130, in __init__
    SemLock.__init__(self, SEMAPHORE, value, value)
  File "/usr/lib64/python2.7/multiprocessing/synchronize.py", line 75, in __init__
    sl = self._semlock = _multiprocessing.SemLock(kind, value, maxvalue)
  OSError: [Errno 28] No space left on device