Zuulv3: add the gate pipeline

Change-Id: Ia870b833802010d0c61d7190835bc8b149f49e34

zuul.yaml

@@ -32,6 +32,50 @@
           status: 'failure'
       mysql:
 
+- pipeline:
+    name: gate
+    description: |
+      Changes that have been approved by core developers are enqueued
+      in order in this pipeline, and if they pass tests, will be
+      merged.
+    success-message: Build succeeded (gate pipeline).
+    failure-message: |
+      Build failed (gate pipeline).  For information on how to proceed, see
+      http://docs.openstack.org/infra/manual/developers.html#automated-testing
+    manager: dependent
+    precedence: high
+    require:
+      gerrit:
+        open: True
+        current-patchset: True
+        approval:
+          - verified: [1, 2]
+            username: zuul
+          - workflow: 1
+    trigger:
+      gerrit:
+        - event: comment-added
+          approval:
+            - workflow: 1
+        - event: comment-added
+          approval:
+            - verified: 1
+          username: zuul
+    start:
+      gerrit:
+        verified: 0
+    success:
+      gerrit:
+        verified: 2
+        submit: true
+      mysql:
+    failure:
+      gerrit:
+        verified: -2
+      mysql:
+    window-floor: 20
+    window-increase-factor: 2
+
 - pipeline:
     name: release
     # NOTE(pabelanger): release pipeline needs access to credentials (eg: pypi).