Use Zuul v3 native job for building scripts

Add a new job that builds the training-labs scripts.

Change-Id: Icdba6792861650f528a3688e9f06b3887670dc96
Needed-By: Id866646c81ccc0c89a24cea006f0df6b23756ece

.zuul.yaml

@@ -0,0 +1,15 @@
+- project:
+    name: openstack/training-labs
+    check:
+      jobs:
+        - training-labs-scripts
+    gate:
+      jobs:
+        - training-labs-scripts
+
+- job:
+    name: training-labs-scripts
+    description: |
+      Build scripts for training-labs repository.
+    parent: unittests
+    run: playbooks/scripts/run.yaml

playbooks/scripts/run.yaml

@@ -0,0 +1,6 @@
+- hosts: all
+  tasks:
+    - name: Run tools/generate-labs
+      command: bash -xe tools/generate-labs '{{ zuul.branch }}'
+      args:
+        chdir: '{{ zuul.project.src_dir }}'