Check for ovs-testcontroller in OVSController

The programe name changed from test-controller to ovs-testcontroller

Reference:
openvswitch/ovs 0bc1b46a38cca06023fdfa5d500c738ccdfa94e7

mininet/node.py

@@ -1426,7 +1426,8 @@ def __init__( self, name, command='ovs-controller', **kwargs ):
     @classmethod
     def isAvailable( cls ):
         return ( quietRun( 'which ovs-controller' ) or
-                 quietRun( 'which test-controller' ) )
+                 quietRun( 'which test-controller' ) or
+                 quietRun( 'which ovs-testcontroller' ) )
 
 class NOX( Controller ):
     "Controller to run a NOX application."