Port test_netapp to Python 3

Port test_netapp to Python 3

* Add close() method to FakeHttplibSocket,
  FakeDirectCmodeHTTPConnection, FakeDirect7modeHTTPConnection
* Replace StringIO() with BytesIO() for socket buffers
* makefile(): ignore optional arguments after mode
* Fix bytes versus Unicode: use bytes for HTTP body. Encode HTTP body
  to UTF-8 and HTTP headers to Latin1.
* tox.ini: add cinder.tests.unit.test_netapp to Python 3.4

Partial-Implements: blueprint cinder-python3
Change-Id: I3dc8c36a84ffbb47be3e85eed34518c6adad48ec