PVServer bind address CLI option

Add the --bind-address command-line option to pvserver. This option allows changing the address bound to the server socket, so that it is not necessarily exposed on all interfaces using INADDR_ANY (0.0.0.0).

This cannot really be tested with the current test infrastructure, you can always try locally: pvserver or pvserver --bind-address 0.0.0.0 should display a socket with local address 0.0.0.0:11111 when running netstat -tl4pn on the same host, and show up on nmap from another reachable host. When running with --bind-address 127.0.0.1 (or any 127.0.0.0/8 address), netstat shows local address 127.0.0.1:11111 and nmap from another host does not find the open socket.