[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/pyvoltha/adapters/kafka/adapter_request_facade.py b/pyvoltha/adapters/kafka/adapter_request_facade.py
old mode 100755
new mode 100644
index 27dd5e7..b27e740
--- a/pyvoltha/adapters/kafka/adapter_request_facade.py
+++ b/pyvoltha/adapters/kafka/adapter_request_facade.py
@@ -18,6 +18,7 @@
 This facade handles kafka-formatted messages from the Core, extracts the kafka
 formatting and forwards the request to the concrete handler.
 """
+from __future__ import absolute_import
 import structlog
 from twisted.internet.defer import inlineCallbacks
 from zope.interface import implementer