define priorities as a property on the test class

This is just cleaner than keeping a global dictionary.
diff --git a/tests/bsn_ipmask.py b/tests/bsn_ipmask.py
index 6a4d389..c3688ba 100644
--- a/tests/bsn_ipmask.py
+++ b/tests/bsn_ipmask.py
@@ -17,10 +17,6 @@
 #@var im_config Local copy of global configuration data
 im_config = None
 
-# For test priority
-#@var test_prio Set test priority for local tests
-test_prio = {}
-
 def test_set_init(config):
     basic.test_set_init(config)
 
@@ -58,6 +54,9 @@
     """
     Exercise BSN vendor extension for configuring IP source/dest match mask
     """
+
+    priority = -1
+
     def bsn_set_ip_mask(self, index, mask):
         """
         Use the BSN_SET_IP_MASK vendor command to change the IP mask for the
@@ -190,6 +189,3 @@
         msg(ip3)
         self.dataplane.send(ports[0], str(pkt3))
         receive_pkt_verify(self, [ports[2]], pkt3, ports[0])
-
-# Don't run by default
-test_prio["BSNConfigIPMask"] = -1