ubuntu 14 code check fixes so travis can pass (#1006)

examples/treeping64.py

@@ -4,7 +4,7 @@
 
 
 from mininet.log import setLogLevel, info
-from mininet.node import UserSwitch, OVSKernelSwitch, Host, Controller
+from mininet.node import UserSwitch, OVSKernelSwitch, Host
 from mininet.topolib import TreeNet
 
 
@@ -18,8 +18,6 @@ class HostV4( Host ):
             self.cmd( 'sysctl -w net.ipv6.conf.' + cfg )
 
 
-
-
 def treePing64():
     "Run ping test on 64-node tree networks."