Fix version unit test on Python 3

With this change, "tox -e py34" now pass.

Changes:

* Replace unichr() with six.unichr()
* Replace StringIO.StringIO() with six.Bytes() in
  nova.crypto.generate_key_pair()
* On Python 3, replace UserDict.IterableUserDict with
  collections.UserDict
* Replace __builtin__.open with six.moves.builtins.open
* Replace ConfigParser import with six.moves.configparser
* On Python 3, get the original "queue" module instead of the "Queue"
  module in nova/virt/libvirt/host.py
* Replace urllib2 with six.moves.urllib
* tox.ini: "tox -e py34" now only runs nova.tests.unit.test_versions

Blueprint nova-python3
Change-Id: I056769c7c5b32276894f7aade8c0a27af81c42ae

nova/version.py

@@ -29,7 +29,7 @@ def _load_config():
     # Don't load in global context, since we can't assume
     # these modules are accessible when distutils uses
     # this module
-    import ConfigParser
+    from six.moves import configparser
 
     from oslo_config import cfg
 
@@ -46,7 +46,7 @@ def _load_config():
         return
 
     try:
-        cfg = ConfigParser.RawConfigParser()
+        cfg = configparser.RawConfigParser()
         cfg.read(cfgfile)
 
         if cfg.has_option("Nova", "vendor"):