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/docker/Dockerfile.openonu_adapter b/python/docker/Dockerfile.openonu_adapter
index 9c42a59..f21cc9f 100644
--- a/python/docker/Dockerfile.openonu_adapter
+++ b/python/docker/Dockerfile.openonu_adapter
@@ -11,26 +11,24 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
-FROM voltha/voltha-python-base:1.0.0
+FROM voltha/voltha-python-base:2.0.0
 
 # Install adapter requirements.
 COPY requirements.txt /tmp/requirements.txt
-RUN pip install -r /tmp/requirements.txt
+RUN pip install --no-cache-dir -r /tmp/requirements.txt
 
 ARG LOCAL_PYVOLTHA
 ARG LOCAL_PROTOS
 COPY local_imports/ /local_imports/
 RUN if [ -n "$LOCAL_PYVOLTHA" ] ; then \
-    pip install /local_imports/pyvoltha/dist/*.tar.gz ; \
+    pip install --no-cache-dir /local_imports/pyvoltha/dist/*.tar.gz ; \
 fi
 
 RUN if [ -n "$LOCAL_PROTOS" ] ; then \
-    pip install /local_imports/voltha-protos/dist/*.tar.gz ; \
+    pip install --no-cache-dir /local_imports/voltha-protos/dist/*.tar.gz ; \
 fi
 
 # Bundle app source
-RUN mkdir /voltha && touch /voltha/__init__.py
-RUN mkdir /voltha/adapters && touch /voltha/adapters/__init__.py
 ENV PYTHONPATH=/voltha
 COPY adapters/brcm_openomci_onu /voltha/adapters/brcm_openomci_onu