Improved FrameIO support and proxy messaging

Specific changes:
- FrameIO support for Mac OS X (making testing easier)
- Message passing between root and child devices implemented
  (example use in simulated_olt and simulated_onu adapters
- Making FrameIOMgr accessible via registry so that modules
  can easily reach it
- Making "main" to be a registered component so that command
  line args and config file based info is accessible to all.
- Minor clean-ups and improvements

Change-Id: I6812dd5b198fef5cb19f17fc8d7948d3fba8b625
diff --git a/env.sh b/env.sh
index 9efac4d..d1d023b 100644
--- a/env.sh
+++ b/env.sh
@@ -13,7 +13,7 @@
 . $VENVDIR/bin/activate
 
 # add top-level voltha dir to pythonpath
-export PYTHONPATH=$VENVDIR/lib/python2.7/site-packages:$PYTHONPATH:$VOLTHA_BASE:$VOLTHA_BASE/voltha/protos/third_party
+export PYTHONPATH=$VOLTHA_BASE/$VENVDIR/lib/python2.7/site-packages:$PYTHONPATH:$VOLTHA_BASE:$VOLTHA_BASE/voltha/protos/third_party
 
 # assign DOCKER_HOST_IP to be the main ip address of this host
 export DOCKER_HOST_IP=$(python common/utils/nethelpers.py)