open log files

def open_telemetry_logs(logpath_telem, logpath_telem_raw):
    '''open log files'''
    if opts.append_log or opts.continue_mode:
        mode = 'a'
    else:
        mode = 'w'
    mpstate.logfile = open(logpath_telem, mode=mode)
    mpstate.logfile_raw = open(logpath_telem_raw, mode=mode)
    print("Log Directory: %s" % mpstate.status.logdir)
    print("Telemetry log: %s" % logpath_telem)

    # use a separate thread for writing to the logfile to prevent
    # delays during disk writes (important as delays can be long if camera
    # app is running)
    t = threading.Thread(target=log_writer, name='log_writer')
    t.daemon = True
    t.start()