Sporadic issues shutting down devstack cleanly

[rossjones]

Sometimes when closing devstack (with ctrl-c) it freezes after displaying "Shutting down devstack". Sometimes, if this is done before the compute nodes are up and running work continues, showing pkg/routing/node_info_publisher.go:106 > failed to publish node info error="context canceled" before freezing.

Often end up having to run kill -9 $(jobs -p) after ctrl-z to recover the terminal.

[wdbaruni]

didn't see this happen for some time, but keeping it open for a little longer

[rossjones]

I implemented #3434 to attempt to resolve this (and related issues), so it may actually be okay now.