add support for undodb debugging server

[fserra]

It would be nice if one could use other debugging servers. Undodb is a nice debugging tool that also provides a server

Thanks!

[fserra]

In bxfi_exec the following options are needed for undodb to work

case BXF_DBG_UNDODB:
    argv[0] = dbg_full;
    argv[argc++] = "--connect-port";
    snprintf(port, sizeof (port), "%d", sandbox->debug.tcp);
    break;