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: I90473fd73a740f2711eb85e131edfa457944ea5e

.zuul.yaml

@@ -15,6 +15,7 @@
       jobs:
         - airship-drydock-omni-test
         - airship-drydock-chart-build-gate
+        - airship-drydock-chart-build-latest-htk
         - airship-drydock-docker-build-gate
 
     gate:
@@ -45,11 +46,22 @@
 
 - job:
     name: airship-drydock-chart-build-gate
+    description: |
+      Builds charts using pinned Helm toolkit.
     timeout: 900
     run: tools/gate/playbooks/build-charts.yaml
     nodeset: airship-drydock-single-node
-    files:
-      - ^charts/.*$
+
+- job:
+    name: airship-drydock-chart-build-latest-htk
+    description: |
+      Builds charts using latest Helm toolkit.
+    timeout: 900
+    voting: false
+    run: tools/gate/playbooks/build-charts.yaml
+    nodeset: airship-drydock-single-node
+    vars:
+      HTK_COMMIT: master
 
 - job:
     name: airship-drydock-docker-build-gate

tools/gate/playbooks/build-charts.yaml

@@ -14,8 +14,11 @@
 
 - hosts: primary
   tasks:
-    - name: Build charts
-      shell: |
-        make charts
-      args:
+    - name: Execute the make target to package Helm charts.
+      make:
         chdir: "{{ zuul.project.src_dir }}"
+        target: charts
+        params:
+          HTK_COMMIT: "{{ HTK_COMMIT | default('') }}"
+      register: result
+      failed_when: result.failed