'/usr/bin/env python' also does not set useful process name for start-stop-daemon

This fixes a regression in commit b10674f3
("re6stnet: new client-only and routing-only mode").

This replaces --connection-count, for more customization, but without requiring
more configuration from the user.

The previous broadcast model is replaced by a query-response one.
During normal operation, the cache of peers is not used anymore to select
peers to connect to. It now only used for bootstrapping and avoid querying
an already known address.

Co-written with Ulysse

using the same socket for sending and listenning

A peer now advertise itself more at the begining to be as present in the local db of other peers than the average