517468 - sw-repo-sync: adding option [-l|--list]

#  spacewalk-repo-sync -l
============================
|   Channel Label   |   Repository   |
============================
test_1 | http://test.repo.rh.com/test_1
test_2 | http://test.repo.rh.com/test_2
test_2 | http://test.repo.rh.com/test_client_2
test_3 | No repository set