Fix ipBase option misspelling

It's arguable that maybe might want to support 'ipbase' as well
since it's used in --ipbase and it's easier to type. However,
ipBase is the spelling used in Mininet, so we should be
consistent.

Change-Id: I2f61df0d2d09abf652c5f06ef9c734a55159a7de

@@ -277,7 +277,7 @@ class ONOSCluster( Controller ):
                 args = ( 1, )
         if not isinstance( topo, Topo ):
             topo = RenamedTopo( topo, *args, hnew='onos', **kwargs )
-        ipBase = kwargs.pop( 'ipbase', '192.168.123.0/24' )
+        ipBase = kwargs.pop( 'ipBase', '192.168.123.0/24' )
         super( ONOSCluster, self ).__init__( name, inNamespace=False )
         fixIPTables()
         self.env = initONOSEnv()