Re-enable test_jobs_launched

This is the traditional "Hello world" of Zuul tests.

This includes some statsd related fixes necessitated by the move
of the pipeline managers into their own module.  It also includes
some fixes to the reconfiguration method to ensure that initial
stats are reported on the initial configuration.

Change-Id: I89d35d3a62b710c1bc768a5d3fac5149859653e1
diff --git a/tests/test_scheduler.py b/tests/test_scheduler.py
index b32f368..1be84a0 100755
--- a/tests/test_scheduler.py
+++ b/tests/test_scheduler.py
@@ -44,8 +44,8 @@
 
 
 class TestScheduler(ZuulTestCase):
+    tenant_config_file = 'config/single-tenant/main.yaml'
 
-    @skip("Disabled for early v3 development")
     def test_jobs_launched(self):
         "Test that jobs are launched and a change is merged"
 
@@ -62,6 +62,7 @@
         self.assertEqual(A.data['status'], 'MERGED')
         self.assertEqual(A.reported, 2)
 
+        # TODOv3(jeblair): we may want to report stats by tenant (also?).
         self.assertReportedStat('gerrit.event.comment-added', value='1|c')
         self.assertReportedStat('zuul.pipeline.gate.current_changes',
                                 value='1|g')