[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/extensions/omci/mock/mock_adapter_agent.py b/test/unit/extensions/omci/mock/mock_adapter_agent.py
index ebe94e2..15bbd60 100644
--- a/test/unit/extensions/omci/mock/mock_adapter_agent.py
+++ b/test/unit/extensions/omci/mock/mock_adapter_agent.py
@@ -14,7 +14,9 @@
 # limitations under the License.
 #
 # import binascii
+from __future__ import absolute_import
 import structlog
+import six
 # from twisted.internet.defer import Deferred
 # from voltha.core.config.config_root import ConfigRoot
 # from pyvoltha.protos.voltha_pb2 import VolthaInstance
@@ -85,7 +87,7 @@
     
     def tearDown(self):
         """Test case cleanup"""
-        for device in self._devices.itervalues():
+        for device in six.itervalues(self._devices):
             device.tearDown()
         self._devices.clear()
 
@@ -115,7 +117,7 @@
             return None
 
         # Get all child devices with the same parent ID
-        children_ids = set(d.id for d in self._devices.itervalues()
+        children_ids = set(d.id for d in six.itervalues(self._devices)
                            if d.parent_id == parent_device_id)
 
         # Loop through all the child devices with this parent ID