CLI hangs after running a plan

[callumforrester]

To reproduce:

(venv) [vid18871@diamrl6120-linux blueapi]$ blueapi -c stomp.yaml controller run count '{"detectors": ["sample_pressure"]}'
INFO:blueapi.messaging.stomptemplate:Connecting...
INFO:stomp.py:established connection to host localhost, port 61613
INFO:blueapi.messaging.stomptemplate:Subscribing to /topic/public.worker.event

I can see the plan runs in the blueapi logs.