Initial confd implementation

ganeti-confd is a simple asynchronous daemon, which listens on a UDP
port, passes each packet to a processor, and sends back to the client
the result.

It also listens on an inotify socket, in order to reload its
configuration when the ganeti config file changes.

Signed-off-by: Guido Trotter <ultrotter@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>