In change I84d2b34d65b3ce7d8d858de106dac531aff509b7, we changed to
call self._converge_create_or_update() in a sub-thread. However,
thread_group_mgr is not set for cancel_update (with rollback),
which in turn calls converge_stack.
This also enables test_cancel_update_server_with_port, as
bug #1607714 seems to be fixed now.
Change-Id: Ie674fd556418f6aa8e79654458cbe43648851db2
Closes-Bug: #1713952