add a new type of RemoteLink in cluster edition that uses GRE tunnels

examples/clusterdemo.py

@@ -3,6 +3,7 @@
 "clusterdemo.py: demo of Mininet Cluster Edition prototype"
 
 from mininet.examples.cluster import MininetCluster, SwitchBinPlacer
+from cluster import RemoteLink, RemoteSSHLink, RemoteGRELink
 from mininet.topolib import TreeTopo
 from mininet.log import setLogLevel
 from mininet.examples.clustercli import ClusterCLI as CLI
@@ -11,7 +12,7 @@ def demo():
     "Simple Demo of Cluster Mode"
     servers = [ 'localhost', 'ubuntu2', 'ubuntu3' ]
     topo = TreeTopo( depth=3, fanout=3 )
-    net = MininetCluster( topo=topo, servers=servers,
+    net = MininetCluster( topo=topo, servers=servers, Link=RemoteLink,
                           placement=SwitchBinPlacer )
     net.start()
     CLI( net )