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.