Adds Support for Managing the Broker API Endpoint IP Address

Previously, the Broker API could only bind to the loopback address
(127.0.0.1).  This makes remotely connecting to the API difficult
by requiring workaround solutions such as SSH tunneling. Since
iptables must allow port 8080, the following commit should also be
accepted for full functionality:

8515ea8c6017c87731fb7dcae86aa8b18b2ba51f

The change introduces the $broker_listen_ip used to specify the IP
address the broker will bind to.  Defaults to '127.0.0.1' for
backwards compatibility.  Note: $broker_ip_addr was not used since
it defaults to $::ipaddress which breaks backwards compatability.