py3: Port pure driver test to Python 3

py3: Port pure driver test to Python 3

* Replace func.func_name with func.__name__: the func_name attribute
  was removed in Python 3, whereas the __name__ attribute exists on
  Python 2 and Python 3
* Create INITIATOR_TARGET_MAP using list(set()) to get the same order
  than the tested code. The exact order is not reliable, it depends
  on the hash function which is now randomized by default on
  Python 3. The hash function is also different between Python 2.7
  and 3.4.
* tox.ini: add test_pure to Python 3.4

Blueprint cinder-python3
Change-Id: I78601278259f1d34ad6ac3458d2dd0a3aca9d77a