Description of problem:
When I'm trying to make a cache of Spacewalk Channel, I see an exception.

Version-Release number of selected component (if applicable):
Spacewalk client 2.5 and 2.6 nightly on Fedora 23

How reproducible:
always

Steps to Reproduce:
1. dnf clean all
2. dnf makecache


Actual results:
Traceback (most recent call last):
  File "/usr/bin/dnf", line 58, in <module>
    main.user_main(sys.argv[1:], exit_code=True)
  File "/usr/lib/python3.4/site-packages/dnf/cli/main.py", line 174, in user_main
    errcode = main(args)
  File "/usr/lib/python3.4/site-packages/dnf/cli/main.py", line 60, in main
    return _main(base, args)
  File "/usr/lib/python3.4/site-packages/dnf/cli/main.py", line 112, in _main
    cli.run()
  File "/usr/lib/python3.4/site-packages/dnf/cli/cli.py", line 1099, in run
    return self.command.run(self.base.extcmds)
  File "/usr/lib/python3.4/site-packages/dnf/cli/commands/makecache.py", line 89, in run
    self.base.fill_sack() # performs the md sync
  File "/usr/lib/python3.4/site-packages/dnf/base.py", line 239, in fill_sack
    self._add_repo_to_sack(r)
  File "/usr/lib/python3.4/site-packages/dnf/base.py", line 111, in _add_repo_to_sack
    repo.load()
  File "/usr/lib/python3.4/site-packages/dnf/repo.py", line 832, in load
    handle = self._handle_new_remote(tmpdir)
  File "/usr/lib/python3.4/site-packages/dnf-plugins/spacewalk.py", line 277, in _handle_new_remote
    self.add_http_headers(handle)
  File "/usr/lib/python3.4/site-packages/dnf-plugins/spacewalk.py", line 259, in add_http_headers
    if not header in self.login_info:
TypeError: argument of type 'NoneType' is not iterable

Expected results:
no errors

Additional info:

If I run 'dnf repolist' cache will be created w/o problems.
Look at line 83 in dnf-plugin-spacewalk/spacewalk.py (class Spacewalk(dnf.Plugin)):

self.activate_channels(self.cli.demands.sack_activation)

if self.cli.demands.sack_activation is False, we do not load login_info from up2date_client.up2dateAuth.getLoginInfo. In case of 'dnf makecache' it is False, in case of 'dnf repolist' it is True.