Change counter frequency interval to seconds - python

The original counter frequency unit was in 1/10 second in pyvoltha.  When the voltha-lib-go library was implemented and used in the OpenOLT golang adapter, it was changed to a 1 second unit.

The 1/10 unit is of very little value and changing the python version to the 1 second unit makes more sense.

This only affects python adapters but the documentation in the pyvoltha markdown should be corrected so that adapters are consistent across different languages.