put createLiveCD tasks in their own channel

docs/schema.sql

@@ -170,6 +170,7 @@ CREATE TABLE channels (
 -- create default channel
 INSERT INTO channels (name) VALUES ('default');
 INSERT INTO channels (name) VALUES ('createrepo');
+INSERT INTO channels (name) VALUES ('livecd');
 
 -- Here we track the build machines
 -- each host has an entry in the users table also

hub/kojihub.py

@@ -4709,7 +4709,7 @@ class RootExports(object):
 
         context.session.assertPerm('livecd')
 
-        taskOpts = {}
+        taskOpts = {'channel': 'livecd'}
         taskOpts['arch'] = arch
         if priority:
             if priority < 0: