Pull values from config file before starting Zyre

Handles these values so far:

    #   Zyre cluster configuration
    zyre
        port = 5670         #   Default = 5670
        interval = 250      #   Default = 1000 msec

Also, if Zyre cannot be started, due to lack of usable network
interface, reports this and in zpipes_test_cluster, does not try
to continue tests. This tracks the latest CZMQ and Zyre masters
which provide this feedback.