Support multiple triggers

Add the ability for Zuul to accept inputs from multiple trigger
sources simultaneously.

Pipelines are associated with exactly one trigger, which must now
be named in the configuration file.

Co-Authored-By: Monty Taylor <mordred@inaugust.com>

Change-Id: Ief2b31a7b8d85d30817f2747c1e2635f71ea24b9
diff --git a/tests/fixtures/layout.yaml b/tests/fixtures/layout.yaml
index ed63e72..675d351 100644
--- a/tests/fixtures/layout.yaml
+++ b/tests/fixtures/layout.yaml
@@ -5,7 +5,8 @@
   - name: check
     manager: IndependentPipelineManager
     trigger:
-      - event: patchset-created
+      gerrit:
+        - event: patchset-created
     success:
       verified: 1
     failure:
@@ -14,16 +15,18 @@
   - name: post
     manager: IndependentPipelineManager
     trigger:
-      - event: ref-updated
-        ref: ^(?!refs/).*$
+      gerrit:
+        - event: ref-updated
+          ref: ^(?!refs/).*$
 
   - name: gate
     manager: DependentPipelineManager
     failure-message: Build failed.  For information on how to proceed, see http://wiki.example.org/Test_Failures
     trigger:
-      - event: comment-added
-        approval:
-          - approved: 1
+      gerrit:
+        - event: comment-added
+          approval:
+            - approved: 1
     success:
       verified: 2
       submit: true
@@ -37,14 +40,16 @@
     manager: IndependentPipelineManager
     dequeue-on-new-patchset: false
     trigger:
-      - event: comment-added
-        approval:
-          - approved: 1
+      gerrit:
+        - event: comment-added
+          approval:
+            - approved: 1
 
   - name: dup1
     manager: IndependentPipelineManager
     trigger:
-      - event: change-restored
+      gerrit:
+        - event: change-restored
     success:
       verified: 1
     failure:
@@ -53,7 +58,8 @@
   - name: dup2
     manager: IndependentPipelineManager
     trigger:
-      - event: change-restored
+      gerrit:
+        - event: change-restored
     success:
       verified: 1
     failure:
@@ -64,9 +70,10 @@
     manager: DependentPipelineManager
     failure-message: Build failed.  For information on how to proceed, see http://wiki.example.org/Test_Failures
     trigger:
-      - event: comment-added
-        approval:
-          - approved: 1
+      gerrit:
+        - event: comment-added
+          approval:
+            - approved: 1
     success:
       verified: 2
       submit: true