Peer discovery ttl configuration flag

[fntlnz]

This exposes a new flag --peerdiscoveryttl and a new env var WIREY_PEERDISCOVERYTTL that can be used to configure how often wirey connects to the backend to get the list of peers.

Example usage:

./bin/wirey --endpoint 192.168.33.11 --ipaddr 10.30.0.10 --http http://192.168.33.10:8080 --httpbasicauth time: --peerdiscoveryttl 1m

Signed-off-by: Lorenzo Fontana lo@linux.com