Add missing start-message in pipeline config schema

Change-Id: I006f92b6ebf4b308425cd70e1d81e26f3e82beaf

tests/fixtures/layouts/start-message.yaml

@@ -0,0 +1,37 @@
+- pipeline:
+    name: gate
+    manager: dependent
+    start-message: Jobs started for {pipeline.name}.
+    trigger:
+      gerrit:
+        - event: comment-added
+          approval:
+            - Approved: 1
+    start:
+      smtp:
+        to: you@example.com
+      gerrit:
+        Verified: 0
+    success:
+      gerrit:
+        Verified: 2
+        submit: true
+    failure:
+      gerrit:
+        Verified: -2
+    precedence: high
+
+- job:
+    name: base
+    parent: null
+    run: playbooks/base.yaml
+
+- job:
+    name: project-test1
+    run: playbooks/project-test1.yaml
+
+- project:
+    name: org/project
+    gate:
+      jobs:
+        - project-test1

tests/unit/test_scheduler.py

@@ -4818,6 +4818,21 @@ For CI problems and help debugging, contact ci@example.org"""
         self.assertFalse(self.smtp_messages[1]['body'].startswith(failure_msg))
         self.assertTrue(self.smtp_messages[1]['body'].endswith(footer_msg))
 
+    @simple_layout('layouts/start-message.yaml')
+    def test_start_message(self):
+        "Test a pipeline's start message is correctly added to the report."
+        A = self.fake_gerrit.addFakeChange('org/project', 'master', 'A')
+        A.addApproval('Code-Review', 2)
+        self.fake_gerrit.addEvent(A.addApproval('Approved', 1))
+        self.waitUntilSettled()
+
+        self.assertEqual(1, len(self.smtp_messages))
+
+        start_msg = """\
+Jobs started for gate."""
+
+        self.assertTrue(self.smtp_messages[0]['body'].startswith(start_msg))
+
     @simple_layout('layouts/unmanaged-project.yaml')
     def test_unmanaged_project_start_message(self):
         "Test start reporting is not done for unmanaged projects."

zuul/configloader.py

@@ -1149,6 +1149,7 @@ class PipelineParser(object):
                     'description': str,
                     'success-message': str,
                     'failure-message': str,
+                    'start-message': str,
                     'merge-failure-message': str,
                     'footer-message': str,
                     'dequeue-on-new-patchset': bool,