dabbad: unlink pidfile only when available.

Signed-off-by: Emmanuel Roullit <emmanuel.roullit@gmail.com>
dabbad: add dabbad rpc server ctor/dtor.

Signed-off-by: Emmanuel Roullit <emmanuel.roullit@gmail.com>
dabbad: destroy the rpc server on signal.

Signed-off-by: Emmanuel Roullit <emmanuel.roullit@gmail.com>
dabbad: do not register dtor on atexit().

The process never ends on its own. Such termination is always triggered
by a signal. Let the signal handler called the destructor and exit the
process.

Signed-off-by: Emmanuel Roullit <emmanuel.roullit@gmail.com>
dabbad: daemonize when the RPC server is ready.

Signed-off-by: Emmanuel Roullit <emmanuel.roullit@gmail.com>