Ensure listener args are always a tuple/immutable
Ensure listener args are always a tuple/immutable

Make sure the arguments are not mutable and can not
be modified by anyone so that the listener maintains
a read-only state after it has been created (immutability
is typically always good & preferred).

Change-Id: I819ea43e6e7e77179e15df3ecbb7c39e96c0592f

jimbobhickville/taskflow,openstack/taskflow,jimbobhickville/taskflow,pombredanne/taskflow-1,junneyang/taskflow,pombredanne/taskflow-1,openstack/taskflow,junneyang/taskflow