grafana: add devstack dashboard

For the start, the dashboard contains a graph that shows failure rates
for each of platforms targeted by check queue (trusty, xenial, centos,
and fedora24). The graph should help us to decide if a new platform is
ready to get its own voting job.

Change-Id: If0a6978668284513c17f69f618c1b75473032378

grafana/devstack.yaml

@@ -0,0 +1,23 @@
+dashboard:
+  title: Devstack Failure Rate
+  rows:
+    - title: Description
+      height: 100px
+      panels:
+        - title: Description
+          content: |
+            **This dashboard is managed by [Grafyaml](http://docs.openstack.org/infra/system-config/grafyaml.html).**
+
+            If you would like to make changes to this dashboard, please see the grafana directory in [project-config](https://git.openstack.org/cgit/openstack-infra/project-config/tree/grafana/neutron.yaml).
+          type: text
+    - title: Graphs
+      height: 320px
+      panels:
+        - title: Platform Tempest Full Failure Rates (Check queue)
+          span: 4
+          targets:
+            - target: alias(movingAverage(asPercent(transformNull(stats_counts.zuul.pipeline.check.job.gate-tempest-dsvm-neutron-full-ubuntu-xenial.FAILURE),sum(stats_counts.zuul.pipeline.check.job.gate-tempest-dsvm-neutron-full-ubuntu-xenial.{SUCCESS,FAILURE})),'24hours'), 'gate-tempest-dsvm-neutron-full-ubuntu-xenial')
+            - target: alias(movingAverage(asPercent(transformNull(stats_counts.zuul.pipeline.check.job.gate-tempest-dsvm-platform-ubuntu-trusty.FAILURE),sum(stats_counts.zuul.pipeline.check.job.gate-tempest-dsvm-platform-ubuntu-trusty.{SUCCESS,FAILURE})),'24hours'), 'gate-tempest-dsvm-platform-ubuntu-trusty')
+            - target: alias(movingAverage(asPercent(transformNull(stats_counts.zuul.pipeline.check.job.gate-tempest-dsvm-platform-centos7-nv.FAILURE),sum(stats_counts.zuul.pipeline.check.job.gate-tempest-dsvm-platform-centos7-nv.{SUCCESS,FAILURE})),'24hours'), 'gate-tempest-dsvm-platform-centos7-nv')
+            - target: alias(movingAverage(asPercent(transformNull(stats_counts.zuul.pipeline.check.job.gate-tempest-dsvm-platform-fedora24-nv.FAILURE),sum(stats_counts.zuul.pipeline.check.job.gate-tempest-dsvm-platform-fedora24-nv.{SUCCESS,FAILURE})),'24hours'), 'gate-tempest-dsvm-platform-fedora24-nv')
+          type: graph