support github pull request labels

Allow to match trigger on adding or removing github labels. Also
reporter can add or remove labels.

Change-Id: Id385b92590e252c283ba3ebe1ecfd33b34469a2e
Co-Authored-By: Jesse Keating <omgjlk@us.ibm.com>
diff --git a/tests/fixtures/layouts/labeling-github.yaml b/tests/fixtures/layouts/labeling-github.yaml
new file mode 100644
index 0000000..33ce993
--- /dev/null
+++ b/tests/fixtures/layouts/labeling-github.yaml
@@ -0,0 +1,29 @@
+- pipeline:
+    name: labels
+    description: Trigger on labels
+    manager: independent
+    trigger:
+      github:
+        - event: pull_request
+          action: labeled
+          label:
+            - 'test'
+        - event: pull_request
+          action: unlabeled
+          label:
+            - 'do not test'
+    success:
+      github:
+        label:
+          - 'tests passed'
+        unlabel:
+          - 'test'
+
+- job:
+    name: project-labels
+
+- project:
+    name: org/project
+    labels:
+      jobs:
+        - project-labels