system instance needs config file

[garlick]

When brokers for the system instance start up, they will need to have at least some minimal information from a config file in order to wire up with the rest of the instance.

At one point we had talked about adding a broker command line option to allow attributes to be set from a config file. This might be sufficient for this case, depending on the specifics of how we implement the system instance bootstrap. Alternatively we could design something more elaborate.

[garlick]

Closing as duplicate of #1236