Fix various Python 3 issues

Fix various Python 3 issues

* Drop exceptions import. Replace exceptions.OSError with OSError.
  The exceptions module was removed in Python 3.
* Replace 8l with 8
* Replace generator.next() with next(generator)
* convert_uuid_to_es_fmt(): use bytes
* Replace function.func_name with function.__name__

This change helps to run tests using "testr run" instead of
testtools.run.

Blueprint cinder-python3
Change-Id: I36476199ef336069669c5bc6cb5c285b21d8116b