Fixed UnicodeEncodeError for Python2 unicode objects

On python2 in case of unicode objects, str() was causing UnicodeEncodeError.
Also utf8 encoding as a default (mostly for Python2)

Change-Id: I64373133f65c5b11daa3462b7c21a55d06738c09

tooz/partitioner.py

@@ -13,6 +13,7 @@
 #    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 #    License for the specific language governing permissions and limitations
 #    under the License.
+import six
 from tooz import hashring
 
 
@@ -53,7 +54,7 @@ class Partitioner(object):
     def _hash_object(obj):
         if hasattr(obj, "__tooz_hash__"):
             return obj.__tooz_hash__()
-        return str(obj).encode()
+        return six.text_type(obj).encode('utf8')
 
     def members_for_object(self, obj, ignore_members=None, replicas=1):
         """Return the members responsible for an object.

tooz/tests/test_partitioner.py

@@ -80,7 +80,7 @@ class TestPartitioner(tests.TestWithCoordinator):
     def test_members_of_object_and_others(self):
         p = self._coord.join_partitioned_group(self.group_id)
         self._add_members(3)
-        o = object()
+        o = six.text_type(u"чупакабра")
         m = p.members_for_object(o)
         self.assertEqual(1, len(m))
         m = m.pop()