Starting ASSETS_FRONTEND when the port's in use doesn't report an error

[rpowis]

Steps to replicate...

$ cd $WORKSPACE/assets-frontend/
$ ./server.sh dev

Then in another shell...

$ sm --start AGENT -f # or any profile with a frontend

gives the output

'ASSETS_FRONTEND' version 'None' started with PID = 6335
Started: ASSETS_FRONTEND
All services passed healthcheck

but running sm -s doesn't list ASSETS_FRONTEND and the URLs 404.

The port conflict on 9032 doesn't get reported.