Added Oracle Unbreakable Linux Network integration

This adds a new plugin to spacewalk-repo-sync to connect directly to the Oracle Unbreakable Linux Network (ULN) via the API, i.e. the Spacewalk Server does not need to be registered to ULN. Valid Oracle ULN CSI credentials need to be configured in /etc/rhn/spacewalk-repo-sync/uln.conf (which is marked read-only to root by default).

To configure a ULN-backed Repository, use a URL in the format: uln:///<uln_channel_label>

**Note:** I had to add a check in reposync.py for uln:// style URLs and override the plugin. This is because the RepoSyncTask in taskomatic hard-codes the --type yum parameter in the call to spacewalk-repo-sync. This is the only way I could get UI/taskomatic-triggered syncs to work.