Fix mn -v by using output() rather than info()

info() doesn't produce any output if it's called at
this point; bug was introduced when we tried to eliminate
print().

bin/mn

@@ -22,7 +22,7 @@ if 'PYTHONPATH' in os.environ:
 
 from mininet.clean import cleanup
 from mininet.cli import CLI as CLI
-from mininet.log import lg, LEVELS, info, debug, warn, error
+from mininet.log import lg, LEVELS, info, debug, warn, error, output
 from mininet.net import Mininet, MininetWithControlNet, VERSION
 from mininet.node import ( Host, CPULimitedHost, Controller, OVSController,
                            Ryu, NOX, RemoteController, findController,
@@ -149,7 +149,7 @@ def addDictOption( opts, choicesDict, default, name, **kwargs ):
 
 def version( *_args ):
     "Print Mininet version and exit"
-    info( "%s\n" % VERSION )
+    output( "%s\n" % VERSION )
     exit()