Add source entries for all Zuul pipelines

Zuul now supports this, but assumes gerrit by default.  Make our
config future-proof by specifying explicitly.

Change-Id: Iefb988578fc3f494ebcdeaf3c4a16c519230ad27

modules/openstack_project/files/zuul/layout.yaml

@@ -6,6 +6,7 @@ pipelines:
     description: Newly uploaded patchsets enter this pipeline to receive an initial +/-1 Verified vote from Jenkins.
     failure-message: Build failed.  For information on how to proceed, see https://wiki.openstack.org/wiki/GerritJenkinsGit#Test_Failures
     manager: IndependentPipelineManager
+    source: gerrit
     precedence: low
     require:
       open: True
@@ -51,6 +52,7 @@ pipelines:
     description: Changes that have been approved by core developers are enqueued in order in this pipeline, and if they pass tests in Jenkins, will be merged.
     failure-message: Build failed.  For information on how to proceed, see https://wiki.openstack.org/wiki/GerritJenkinsGit#Test_Failures
     manager: DependentPipelineManager
+    source: gerrit
     precedence: normal
     require:
       open: True
@@ -85,6 +87,7 @@ pipelines:
   - name: post
     description: This pipeline runs jobs that operate after each change is merged.
     manager: IndependentPipelineManager
+    source: gerrit
     precedence: low
     trigger:
       gerrit:
@@ -94,6 +97,7 @@ pipelines:
   - name: tag
     description: This pipeline runs jobs in response to any tag event.
     manager: IndependentPipelineManager
+    source: gerrit
     precedence: high
     trigger:
       gerrit:
@@ -103,6 +107,7 @@ pipelines:
   - name: pre-release
     description: This pipeline runs jobs on projects in response to pre-release tags.
     manager: IndependentPipelineManager
+    source: gerrit
     precedence: high
     trigger:
       gerrit:
@@ -112,6 +117,7 @@ pipelines:
   - name: release
     description: When a commit is tagged as a release, this pipeline runs jobs that publish archives and documentation.
     manager: IndependentPipelineManager
+    source: gerrit
     precedence: high
     trigger:
       gerrit:
@@ -121,6 +127,7 @@ pipelines:
   - name: silent
     description: This pipeline is used for silently testing new jobs.
     manager: IndependentPipelineManager
+    source: gerrit
     precedence: low
     trigger:
       gerrit:
@@ -131,6 +138,7 @@ pipelines:
   - name: experimental
     description: On-demand pipeline for requesting a run against a set of jobs that are not yet gating. Leave review comment of "check experimental" to run jobs in this pipeline.
     manager: IndependentPipelineManager
+    source: gerrit
     precedence: low
     trigger:
       gerrit:
@@ -144,6 +152,7 @@ pipelines:
   - name: periodic
     description: Jobs in this queue are triggered on a timer.
     manager: IndependentPipelineManager
+    source: gerrit
     precedence: low
     trigger:
       timer:
@@ -152,6 +161,7 @@ pipelines:
   - name: periodic-stable
     description: Periodic checks of the stable branches.
     manager: IndependentPipelineManager
+    source: gerrit
     precedence: low
     trigger:
       timer:
@@ -165,6 +175,7 @@ pipelines:
   - name: periodic-qa
     description: Periodic jobs for the QA team.
     manager: IndependentPipelineManager
+    source: gerrit
     precedence: low
     trigger:
       timer:
@@ -187,6 +198,7 @@ pipelines:
       Build failed.  For information on how to proceed, see
       https://wiki.openstack.org/wiki/GerritJenkinsGit#Test_Failures
     manager: IndependentPipelineManager
+    source: gerrit
     precedence: low
     require:
       open: True
@@ -208,6 +220,7 @@ pipelines:
       jobs - slower and running without redundancy - so not yet gating. Leave
       review comment of "check experimental" to run jobs in this pipeline.
     manager: IndependentPipelineManager
+    source: gerrit
     precedence: low
     trigger:
       gerrit: