Enable test_multi_branch cloner/executor test

This changes the method of evaluation to verify that commits are
present rather than checking for ZUUL_COMMIT -- that variable is
no longer correct as, in the case of a merge commit, it represents
the SHA which was generated on the merger, which will not be the
same SHA generated on the executor.

The *content*, however, will be the same.

Change-Id: I4bed780c75ef9e586b3cfce2a88322dcaf9df1d5
diff --git a/tests/fixtures/layouts/repo-checkout-four-project.yaml b/tests/fixtures/layouts/repo-checkout-four-project.yaml
new file mode 100644
index 0000000..392931a
--- /dev/null
+++ b/tests/fixtures/layouts/repo-checkout-four-project.yaml
@@ -0,0 +1,81 @@
+- pipeline:
+    name: check
+    manager: independent
+    trigger:
+      gerrit:
+        - event: patchset-created
+    success:
+      gerrit:
+        verified: 1
+    failure:
+      gerrit:
+        verified: -1
+
+- pipeline:
+    name: gate
+    manager: dependent
+    success-message: Build succeeded (gate).
+    trigger:
+      gerrit:
+        - event: comment-added
+          approval:
+            - approved: 1
+    success:
+      gerrit:
+        verified: 2
+        submit: true
+    failure:
+      gerrit:
+        verified: -2
+    start:
+      gerrit:
+        verified: 0
+    precedence: high
+
+- job:
+    name: integration
+    required-projects:
+      - org/project1
+      - org/project2
+      - org/project3
+      - org/project4
+
+- project:
+    name: org/project1
+    check:
+      jobs:
+        - integration
+    gate:
+      queue: integrated
+      jobs:
+        - integration
+
+- project:
+    name: org/project2
+    check:
+      jobs:
+        - integration
+    gate:
+      queue: integrated
+      jobs:
+        - integration
+
+- project:
+    name: org/project3
+    check:
+      jobs:
+        - integration
+    gate:
+      queue: integrated
+      jobs:
+        - integration
+
+- project:
+    name: org/project4
+    check:
+      jobs:
+        - integration
+    gate:
+      queue: integrated
+      jobs:
+        - integration