[VOL-2241] Python 3 refactor of pyvoltha

Majority of work was manual fixes to bytes and strings types, which are
different in py3, but same in py2. As the OMCI library does a lot of
these comparisons and scapy then renders packets, this was frequently
nontrival to debug.

Also:

- Removed grpc dep which wasn't being used, not py3 compatible
- s/Alarms/Events/ to work with protobuf changes per VOL-2224
- Automatic fixes via modernize tooling
- Removed unused OrderedWeakValueDict code
- Removed frameio send_frame specific to Darwin (MacOS), which had no
  corresponding linux code
- Use library functions for hex and unicode conversions
- Various other cleanups and fixes (EOL whitespace, etc.)

Also more (Matt):

 - handle stringify better, check if already string
 - use binary string for binary work
 - import new thread paths
 - update requirements.txt for newer libraries needed with newer python
 - return proper tuple for unpacking
 - bytes string formatting fixed
 - fix mock task unit test

Even more (Zack):

- Python 2/3 compat for _thread by using 'future'
- Bump version to 2.3.0

Change-Id: I53b596d374a944bfb80d0b112f21bcc1f8bcee6e
diff --git a/test/unit/common/test_event_bus.py b/test/unit/common/test_event_bus.py
index be325e8..c833bf0 100644
--- a/test/unit/common/test_event_bus.py
+++ b/test/unit/common/test_event_bus.py
@@ -13,6 +13,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 #
+from __future__ import absolute_import
 import re
 
 from mock import Mock
@@ -21,6 +22,7 @@
 from twisted.trial.unittest import TestCase
 
 from pyvoltha.common.event_bus import EventBusClient, EventBus
+from six.moves import range
 
 
 class TestEventBus(TestCase):
@@ -187,11 +189,11 @@
 
         ebc.subscribe('', lambda _, msg: queue.put(msg))
 
-        for i in xrange(10):
+        for i in range(10):
             ebc.publish('', i)
 
         self.assertEqual(len(queue.pending), 10)
-        for i in xrange(10):
+        for i in range(10):
             msg = yield queue.get()
             self.assertEqual(msg, i)
         self.assertEqual(len(queue.pending), 0)