Remove org_unknown git repo from single-client test config

This was used by two tests to simulate a repo that Zuul doesn't know about.
Using simple_layout is not appropriate here because that would add it to
Zuul's configuration.  The tests aren't structurally a great fit for moving
to a new class with a dedicated config directory, so instead, just make
init_repo work for creating the unknown repo in the fake gerrit without
including it in Zuul's configuration (which is closer to what the test did
in v2).

Change-Id: I60d8897152e3fcfe48f85554604815b3ef86c5b3
diff --git a/tests/base.py b/tests/base.py
index eca0087..9c53846 100755
--- a/tests/base.py
+++ b/tests/base.py
@@ -1658,7 +1658,7 @@
     def assertCleanShutdown(self):
         pass
 
-    def init_repo(self, project):
+    def init_repo(self, project, tag=None):
         parts = project.split('/')
         path = os.path.join(self.upstream_root, *parts[:-1])
         if not os.path.exists(path):
@@ -1672,6 +1672,8 @@
 
         repo.index.commit('initial commit')
         master = repo.create_head('master')
+        if tag:
+            repo.create_tag(tag)
 
         repo.head.reference = master
         zuul.merger.merger.reset_repo_to_head(repo)