Add ability to read custom Mininets

custom/README

@@ -0,0 +1,9 @@
+This directory should hold configuration files for custom mininets.
+
+See custom_example.py, which loads the default minimal topology.  The advantage of defining a mininet in a separate file is that you then use the --custom option in mn_run.py to run the CLI or specific tests with it.
+
+Each custom file must define a Mininet object for an 'mn' variable.
+
+To start up a mininet with this custom topology, do:
+  sudo mn_run.py --custom custom_example.py
+

custom/custom_example.py

@@ -0,0 +1,25 @@
+'''Example of custom topo
+
+@author Brandon Heller (brandonh@stanford.edu)
+
+'''
+
+from mininet.topo import SingleSwitchTopo
+from mininet.net import Mininet
+from mininet.node import KernelSwitch, Host, Controller, ControllerParams
+
+topo = SingleSwitchTopo(k = 2) # build topology object
+switch = KernelSwitch
+host = Host
+controller = Controller
+controller_params = ControllerParams(0x0a000000, 8) # 10.0.0.0/8
+in_namespace = False
+xterms = False
+mac = True
+arp = True
+
+mn = Mininet(topo, switch, host, controller, controller_params,
+             in_namespace = in_namespace,
+             xterms = xterms, auto_set_macs = mac,
+             auto_static_arp = arp)
+