Add configurable footer-message reports

Currently there is no way to add extra information to the end of a
report sent back by zuul. This adds a 'footer-message' field to the
pipelines allowing operators to leave extra information at the end
of a build result.

This is useful for leaving CI contact and debugging information.

Change-Id: Ieae62e845915fa3997353b6b425e215966a9338c
diff --git a/tests/fixtures/layout-footer-message.yaml b/tests/fixtures/layout-footer-message.yaml
new file mode 100644
index 0000000..7977c19
--- /dev/null
+++ b/tests/fixtures/layout-footer-message.yaml
@@ -0,0 +1,34 @@
+includes:
+  - python-file: custom_functions.py
+
+pipelines:
+  - name: gate
+    manager: DependentPipelineManager
+    failure-message: Build failed.  For information on how to proceed, see http://wiki.example.org/Test_Failures
+    footer-message: For CI problems and help debugging, contact ci@example.org
+    trigger:
+      gerrit:
+        - event: comment-added
+          approval:
+            - approved: 1
+    success:
+      gerrit:
+        verified: 2
+        submit: true
+      smtp:
+        to: success@example.org
+    failure:
+      gerrit:
+        verified: -2
+      smtp:
+        to: failure@example.org
+    start:
+      gerrit:
+        verified: 0
+    precedence: high
+
+projects:
+  - name: org/project
+    gate:
+      - test1
+      - test2