openDHT initialization
Issue generated from Tuleap's migration script. Originally submitted by: lightzhan (liangzhan)
For avoiding the ISP masking the opendht bootrap server, I suggest that when the software start, if it can not connect to the server, it will try to connect to the node that it found last time. If so, we can connect to the server with proxy or vpn at the first time but do not need next time.