Make Ripcord-specific topologies optional

If ripcord.dctopo imports properly, then include its topologies in the
list of available ones.  Also replace topo.py with new generic
topologies and update paths.

mininet/test/test_nets.py

@@ -7,16 +7,14 @@ Test creation and all-pairs ping for each included mininet topo type.
 from time import sleep
 import unittest
 
-from ripcord.topo import SingleSwitchTopo, LinearTopo
-
 from mininet.net import init, Mininet
-from mininet.node import KernelSwitch, Host, ControllerParams
-from mininet.node import Controller
-from mininet.topo import TreeTopo
+from mininet.node import KernelSwitch, Host, Controller, ControllerParams
+from mininet.topo import SingleSwitchTopo, LinearTopo
 
 # temporary, until user-space side is tested
 SWITCHES = {'kernel' : KernelSwitch}
 
+
 class testSingleSwitch(unittest.TestCase):
     '''For each datapath type, test ping with single switch topologies.'''
 
@@ -55,20 +53,5 @@ class testLinear(unittest.TestCase):
             self.assertEqual(dropped, 0)
 
 
-class testTree(unittest.TestCase):
-    '''For each datapath type, test all-pairs ping with TreeNet.'''
-
-    def testTree9(self):
-        '''Ping test with both datapaths on 9-host topology'''
-        init()
-        for switch in SWITCHES.values():
-            controller_params = ControllerParams(0x0a000000, 8) # 10.0.0.0/8
-            tree_topo = TreeTopo(depth = 3, fanout = 3)
-            mn = Mininet(tree_topo, switch, Host, Controller,
-                         controller_params)
-            dropped = mn.run('ping')
-            self.assertEqual(dropped, 0)
-
-
 if __name__ == '__main__':
     unittest.main()