Fix Python 3 issues in the blockbridge driver

Fix Python 3 issues in the blockbridge driver

* Replace httplib import with six.moves.http_client
* Replace urllib imports with six.moves.urllib, update urllib.
  For example, replace urllib.quote() with urllib.parse.quote().
* test_blockbridge: try get the mock module from unittest.mock, part of
  the Python stdlib since Python 3.3. The third-party mock module has a
  bug on Python 3.4.
* On Python 3, base64.encodestring() expects bytes and returns bytes.
  Encode credentials to UTF-8 and decode base64 from ASCII to get the
  final string as Unicode on Python 3.
* test_cfg_api_auth_scheme_password: parse the connection URL to compare
  it. Comparing directly the URL fails on Python 3 because URL
  parameters are rendered in a random order because of the hash
  randomization.
* Replace pools.values()[0] with list(pools.values())[0]. On Python 3,
  dict.values() returns an iterator.
* tox.ini: add cinder.tests.unit.test_blockbridge to Python 3.4.

Blueprint cinder-python3
Change-Id: I3c6b935680b5427d6ffdc1a00cd5221475209cdd