Handle SIGINT different

Don't try to trap the signal and bail out gracefully.  Things
seem to work more reliably if we just let SIGINT do it's thing.
otherwise we wend up hanging on the unfinished READ that may
not happen
Allow device id to be chosen

If you have multiple BT devices you may want to choose the one
to do the scanning on.  Not specifying a device id tells bluez
to try to autoselect the first available device.