CI: Run yamllint on added or modified YAML files

Signed-off-by: Nils Philippsen <nils@redhat.com>

.yamllint.yaml

@@ -0,0 +1,14 @@
+---
+extends: default
+
+rules:
+  indentation:
+    spaces: 2
+    indent-sequences: whatever
+    level: warning
+  line-length:
+    max: 100
+    level: warning
+  truthy:
+    allowed-values: ['true', 'false', 'yes', 'no']
+...

.zuul.yaml

@@ -19,8 +19,16 @@
     parent: fi-ansible--ansible-review-base
     run: ci/ansible-review-diff.yaml
 
+- job:
+    name: fi-ansible--yamllint-diff
+    run: ci/yamllint-diff.yaml
+    files:
+      - \.yml$
+      - \.yaml$
+
 - project:
     check:
       jobs:
         - fi-ansible--zuul-jobs-verify-namespace
         - fi-ansible--ansible-review-diff
+        - fi-ansible--yamllint-diff

ci/yamllint-diff.yaml

@@ -0,0 +1,24 @@
+---
+- hosts: all
+  tasks:
+    - name: Install yamllint
+      package:
+        name: yamllint
+        state: latest
+
+    - name: Determine added or modified YAML files
+      command:
+        cmd: >
+          git diff --name-only --diff-filter=AM
+          origin/{{ zuul.branch|quote }}...{{ zuul.branch|quote }}
+      args:
+        chdir: '{{ zuul.project.src_dir }}'
+      register: fi_ansible__added_modified_yaml_files
+      changed_when: "False"
+      failed_when: fi_ansible__added_modified_yaml_files.rc != 0
+
+    - name: Run yamllint on changed YAML files
+      command: yamllint {{ item }}
+      args:
+        chdir: '{{ zuul.project.src_dir }}'
+      with_items: "{{ fi_ansible__added_modified_yaml_files.stdout_lines | list }}"