[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/dev/mininet/examples/multicluster.py b/tools/dev/mininet/examples/multicluster.py
index 29e2b56..1ad7c5b 100755
--- a/tools/dev/mininet/examples/multicluster.py
+++ b/tools/dev/mininet/examples/multicluster.py
@@ -1,5 +1,4 @@
-#!/usr/bin/python
-
+#!/usr/bin/python3
 """
 multicluster.py: multiple ONOS clusters example
 
@@ -85,7 +84,7 @@
         cmap.setdefault( c, [] ).append( s.name )
     for c in sorted( cmap.keys() ):
         switches = ' '.join( cmap[ c ] )
-        print '%s: %s' % ( c, switches )
+        print('%s: %s' % ( c, switches ))
 
 ONOSCLI.do_controllers = do_controllers