modify zenhub healthcheck - use pb, rather than grep.

Collectors always use the default localhost:8789. Changing it to use a different port is more involved in Europa land so I don't think it would generally be done.

It is possible to change the conf for a collector to point to another IP and port, that probably wouldn't work since the IPs of the containers aren't generally routable from other hosts.

If the just the hub port was changed in the collector conf then the service definition would have to change to import the new port.