print -> info; end the horror of print vs. print()

Although we could use print() from __future__, this messes
up scripts which use examples as modules.

The simple, if not nicest for 2.7, solution is to use
info(), output() and other mininet.log functions. The disadvantage
is that we may have to adjust things if we change info() to
add automatic newlines, but we can burn that bridge in Mininet
3.x.

examples/popenpoll.py

@@ -2,34 +2,35 @@
 
 "Monitor multiple hosts using popen()/pmonitor()"
 
-
 from mininet.net import Mininet
 from mininet.topo import SingleSwitchTopo
 from mininet.util import pmonitor
+from mininet.log import setLogLevel, info
+
 from time import time
 from signal import SIGINT
 
-
 def pmonitorTest( N=3, seconds=10 ):
     "Run pings and monitor multiple hosts using pmonitor"
     topo = SingleSwitchTopo( N )
     net = Mininet( topo )
     net.start()
     hosts = net.hosts
-    print( "Starting test..." )
+    info( "Starting test...\n" )
     server = hosts[ 0 ]
     popens = {}
     for h in hosts:
         popens[ h ] = h.popen('ping', server.IP() )
-    print( "Monitoring output for", seconds, "seconds" )
+    info( "Monitoring output for", seconds, "seconds\n" )
     endTime = time() + seconds
     for h, line in pmonitor( popens, timeoutms=500 ):
         if h:
-            print( '<%s>: %s' % ( h.name, line ) )
+            info( '<%s>: %s' % ( h.name, line ) )
         if time() >= endTime:
             for p in popens.values():
                 p.send_signal( SIGINT )
     net.stop()
 
 if __name__ == '__main__':
+    setLogLevel( 'info' )
     pmonitorTest()