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/test/test_multipoll.py

@@ -16,7 +16,7 @@ class testMultiPoll( unittest.TestCase ):
                  "(h\d+): \d+ bytes from",
                  "Monitoring output for (\d+) seconds",
                  pexpect.EOF ]
-        pings = {}
+        pings, seconds = {}, -1
         while True:
             index = p.expect( opts )
             if index == 0:
@@ -32,7 +32,8 @@ class testMultiPoll( unittest.TestCase ):
         self.assertTrue( len( pings ) > 0 )
         # make sure we have received at least one ping per second
         for count in pings.values():
-            self.assertTrue( count >= seconds )
+            self.assertTrue( count >= seconds,
+                             '%d pings < %d seconds' % ( count, seconds ) )
 
 if __name__ == '__main__':
     unittest.main()