VOL-2241:  Python 3 migration

 - rename adapter class file and remove unneeded __init__ to make imports work without major rearrange
 - venv and Dockerfile fixups needed for new pyvoltha (cannot install old first)
 - clean up yaml config file as it contained empty entries that failed to parse
 - clean up imports
 - remove itervalues iter*
 - convert to list() as needed
 - test with python 3.6
 - skip non-dict items in tcont loop
 - update to voltha-protos 2.1.0
 - migrate socketserver and simplehttpserver to python3 import

Change-Id: Id8efa72b6796a3055b1927716503a33544bb6548
diff --git a/python/Makefile b/python/Makefile
index 98005d2..c505319 100644
--- a/python/Makefile
+++ b/python/Makefile
@@ -96,9 +96,8 @@
 VENVDIR := venv-openonu
 
 venv: distclean local-protos local-pyvoltha
-	virtualenv ${VENVDIR};\
+	virtualenv --python=python3.6 ${VENVDIR};\
         source ./${VENVDIR}/bin/activate ; set -u ;\
-	rm ${VENVDIR}/local/bin ${VENVDIR}/local/lib ${VENVDIR}/local/include ;\
         pip install -r requirements.txt
 
 ifdef LOCAL_PYVOLTHA