fix reconfig priorities

The reconfig code was sorting services in the reverse of the direction
the docs -- and all users of the priority -- indicated.

master/buildbot/config.py

@@ -700,7 +700,7 @@ def reconfigService(self, new_config):
                 if isinstance(svc, ReconfigurableServiceMixin) ]
 
         # sort by priority
-        reconfigurable_services.sort(key=lambda svc : svc.reconfig_priority)
+        reconfigurable_services.sort(key=lambda svc : -svc.reconfig_priority)
 
         for svc in reconfigurable_services:
             d = svc.reconfigService(new_config)

master/buildbot/test/unit/test_config.py

@@ -1074,7 +1074,6 @@ def test_multiservice_priority(self):
         @d.addCallback
         def check(_):
             prio_order = [ svc.called for svc in services ]
-            prio_order.reverse()
             called_order = sorted(prio_order)
             self.assertEqual(prio_order, called_order)
         return d