CI: Add chart build job for latest Helm toolkit

This commit introduces a non-voting job to lint Helm charts against the
latest version of Helm toolkit from OpenStack-Helm Infra. This job
should serve as an indicator of when it's safe to advance the version of
Helm toolkit used by Airship.

Additionally, this commit modifies all Helm chart lint jobs to run on
each commit, regardless of the files modified by a change. This should
not introduce a noticeable difference in CI runtime, as these jobs
execute quicker than the tox jobs.

Change-Id: I43e9ef816317d20277bd951b97fd059ec472a234

.zuul.yaml

@@ -14,12 +14,13 @@
     check:
       jobs:
         - airship-maas-lint-ws
-        - airship-maas-lint-chart
+        - airship-maas-chart-build-gate
+        - airship-maas-chart-build-latest-htk
         - airship-maas-docker-build-gate
     gate:
       jobs:
         - airship-maas-lint-ws
-        - airship-maas-lint-chart
+        - airship-maas-chart-build-gate
         - airship-maas-docker-build-gate
     post:
       jobs:
@@ -40,15 +41,22 @@
     nodeset: airship-maas-single-node
 
 - job:
-    name: airship-maas-lint-chart
-    files:
-      - ^charts/.*$
-    description: |
-      Lints Helm charts for validity
+    name: airship-maas-chart-build-gate
+    description: Build charts using pinned Helm toolkit.
     run: tools/gate/playbooks/helm-linter.yaml
     timeout: 600
     nodeset: airship-maas-single-node
 
+- job:
+    name: airship-maas-chart-build-latest-htk
+    description: Build charts using latest Helm toolkit.
+    voting: false
+    run: tools/gate/playbooks/helm-linter.yaml
+    timeout: 600
+    nodeset: airship-maas-single-node
+    vars:
+      HTK_COMMIT: master
+
 - job:
     name: airship-maas-docker-build-gate
     timeout: 1800

tools/gate/playbooks/helm-linter.yaml

@@ -13,9 +13,11 @@
 
 - hosts: primary
   tasks:
-    - name: Execute the make target for Helm chart linting
+    - name: Execute the make target to package Helm charts.
       make:
         chdir: "{{ zuul.project.src_dir }}"
-        target: helm_lint
+        target: charts
+        params:
+          HTK_COMMIT: "{{ HTK_COMMIT | default('') }}"
       register: result
       failed_when: result.failed