* Calculate sampling error rate over a time window

* Create the following variables to control bert testing behavior:
  bert_timeout_ms - Milliseconds to wait for bert sync before timing out
  bert_window_ms - Window of time to calculate sampling error rate percentage
  bert_max_err - Max percentage of error tolerated before going out of sync
  bert_hangup_on_error - Hangup when error occurs (Timeout or going out of sync)