Can't quit `ceph-salt apply` if it's waiting for node reboots

[tserong]

Ran ceph-salt apply, it got to the point of rebooting various nodes, and I realised there was no way to quit, while the UI was still spinning waiting for those rebooted nodes to come back. 'Q' did nothing, CTRL-C did nothing, IIRC I had to CTRL-Z then kill it. Should there be a way to quit in this case (or in any case where execution is not yet complete)?