changed deprecated channel_label attribute

library/packaging/rhn_channel

@@ -89,6 +89,9 @@ def unsubscribe_channels(channels, client, session, sysname, sys_id):
 
 def base_channels(client, session, sys_id):
     basechan = client.channel.software.listSystemChannels(session, sys_id)
+    try:
+        chans = [item['label'] for item in basechan]
+    except KeyError:
         chans = [item['channel_label'] for item in basechan]
     return chans