add a global config dictionary

There was no need for each test module to keep a copy for itself. This means we
can also get rid of test_set_init.
diff --git a/tests/bsn_ipmask.py b/tests/bsn_ipmask.py
index c3688ba..ce785c9 100644
--- a/tests/bsn_ipmask.py
+++ b/tests/bsn_ipmask.py
@@ -4,6 +4,7 @@
 
 import logging
 
+from oftest import config
 import oftest.controller as controller
 import oftest.cstruct as ofp
 import oftest.message as message
@@ -11,21 +12,6 @@
 
 from oftest.testutils import *
 
-#@var port_map Local copy of the configuration map from OF port
-# numbers to OS interfaces
-im_port_map = None
-#@var im_config Local copy of global configuration data
-im_config = None
-
-def test_set_init(config):
-    basic.test_set_init(config)
-
-    global im_port_map
-    global im_config
-
-    im_port_map = config["port_map"]
-    im_config = config
-
 def normal_ip_mask(index):
     """
     Return the IP mask for the given wildcard index 0 - 63 per the OF 1.0 spec
@@ -125,7 +111,7 @@
                 self.check_ip_mask(False, index, mask)
 
     def check_ip_mask(self, source, index, mask):
-        ports = im_port_map.keys()
+        ports = config["port_map"].keys()
 
         # For each mask we install two flow entries, one which matches
         # on IP source or dest addr all-0s (modulo the mask) and