Implemented main event loop in b10-dhcp-ddns
Added main process event loop to D2Process which is the primary application "object" in b10-dchp-ddns. Along the way it was necessary to adjust D2QueueManager to treat stopping as an asyncrhonous event when IO is pending. This requied a change in lib-dchp-ddns to have awareness of when IO is pending. Fixed a bug in D2 configuration parsing in which parsing a a subsequent configuration caused duplicate TSIGKeyInfo entries.