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/adapters/brcm_openomci_onu/pon_port.py b/python/adapters/brcm_openomci_onu/pon_port.py
index 5c8c7eb..5ed28b2 100644
--- a/python/adapters/brcm_openomci_onu/pon_port.py
+++ b/python/adapters/brcm_openomci_onu/pon_port.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 structlog
 from twisted.internet.defer import inlineCallbacks, returnValue
 from voltha_protos.common_pb2 import AdminState, OperStatus