Added per-test priority support

In each module, a variable test_prio[] may be added which
is indexed by the test name.

Currently the only application of this is to exclude tests
from the "default" set of tests that are run:  If a test
has a negative priority, then it is not run by default.  This
addresses the issue with "fill exact match table" taking almost
an hour to run.
diff --git a/tests/caps.py b/tests/caps.py
index 1146cf1..439c434 100644
--- a/tests/caps.py
+++ b/tests/caps.py
@@ -25,6 +25,9 @@
 #@var caps_config Local copy of global configuration data
 caps_config = None
 
+# For test priority
+test_prio = {}
+
 def test_set_init(config):
     """
     Set up function for caps test classes
@@ -93,7 +96,7 @@
     while True:
         request.match.nw_src += 1
         rv = obj.controller.message_send(request)
-        do_barrier(obj.controller)
+#        do_barrier(obj.controller)
         flow_count += 1
         if flow_count % count_check == 0:
             response, pkt = obj.controller.transact(tstats, timeout=2)
@@ -133,6 +136,7 @@
         caps_logger.info("Running " + str(self))
         flow_caps_common(self)
 
+test_prio["FillTableExact"] = -1
 
 class FillTableWC(basic.SimpleProtocol):
     """