tests/vhost-user-bridge: read command line arguments

tests/vhost-user-bridge: read command line arguments

Now some vhost-user-bridge parameters can be passed from the
command line:

Usage: prog [-u ud_socket_path] [-l lhost:lport] [-r rhost:rport]
        -u path to unix doman socket. default: /tmp/vubr.sock
        -l local host and port. default: 127.0.0.1:4444
        -r remote host and port. default: 127.0.0.1:5555

Signed-off-by: Victor Kaplansky <victork@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>