Re-enable TestMergerRepo() class for testing

Update the unit test to use the new tenant_config_file for zuulv3.

Change-Id: I5fc2f56647b3e6e05f68607c584d8f594f24aeee
Signed-off-by: Paul Belanger <pabelanger@redhat.com>
diff --git a/tests/test_merger_repo.py b/tests/test_merger_repo.py
index 7bf08ee..5062c14 100644
--- a/tests/test_merger_repo.py
+++ b/tests/test_merger_repo.py
@@ -31,14 +31,12 @@
 class TestMergerRepo(ZuulTestCase):
 
     log = logging.getLogger("zuul.test.merger.repo")
+    tenant_config_file = 'config/single-tenant/main.yaml'
     workspace_root = None
 
     def setUp(self):
-        self.skip("Disabled for early v3 development")
-
-    # def setUp(self):
-    #     super(TestMergerRepo, self).setUp()
-    #     self.workspace_root = os.path.join(self.test_root, 'workspace')
+        super(TestMergerRepo, self).setUp()
+        self.workspace_root = os.path.join(self.test_root, 'workspace')
 
     def test_ensure_cloned(self):
         parent_path = os.path.join(self.upstream_root, 'org/project1')