[WIP] ONOS-8091 Port python script and utilities to python3

Steps performed so far:
- Updated bash scripts and similar to explicitly invoke python3 (instead of python)
- Updated all python scripts using 2to3

Testing these changes will be a major headache because:
- different scripts are executed in different environments
  (e.g., Jenkins, cell servers, tutorial VMs, etc.)
- we don’t have control on all environments
- some environments we used to control have been dismissed
  (e.g., cell servers)

The approach for now is to focus on the essentials:
- Jenkins jobs for pre-merge and release

Test and fix everything else as the need arises.

Change-Id: I943e214760c9dea9a7ded0d47ef08adbc0ed0bec
diff --git a/tools/test/topos/opticalTest.py b/tools/test/topos/opticalTest.py
index 8e316fa..2f94747 100755
--- a/tools/test/topos/opticalTest.py
+++ b/tools/test/topos/opticalTest.py
@@ -1,4 +1,4 @@
-#!/usr/bin/python
+#!/usr/bin/python3
 
 from opticalUtils import MininetOE, LINCSwitch, LINCLink
 from mininet.topo import Topo
@@ -86,8 +86,8 @@
     if len( sys.argv ) >= 2:
         controllers = sys.argv[1:]
     else:
-        print 'Usage:sudo -E python opticalTest.py (<Controller IP>)+'
-        print 'Using localhost...\n'
+        print('Usage:sudo -E python3 opticalTest.py (<Controller IP>)+')
+        print('Using localhost...\n')
         controllers = [ '127.0.0.1' ]
 
     setLogLevel( 'info' )