feat(travis): use conditional to provide one or two lint jobs

* Main goal:   one lint job
* Alternative: split `rubocop` into a separate lint job (`allow_failures`)
* Long-term:   to be able to fully revert this commit when a single lint
               job can be use for all formulas

ssf/defaults.yaml

@@ -180,6 +180,7 @@ ssf_node_anchors:
         travis:
           addons: {}
           dist: bionic
+          use_single_job_for_linters: true
         use_cirrus_ci: false
         use_tofs: false
         yamllint:

ssf/files/default/.travis.yml

@@ -2,6 +2,31 @@
 # vim: ft=yaml
 ---
 {%- from tplroot ~ "/libcimatrix.jinja" import format_ci_matrix with context %}
+
+{%- macro format_allow_failures(use_single_job_for_linters) %}
+{%-   filter indent(2) %}
+{%-     if not use_single_job_for_linters %}
+allow_failures:
+  - env: Lint_rubocop
+fast_finish: true
+{%-     endif %}
+{%-   endfilter %}
+{%- endmacro %}
+
+{%- macro format_rubocop_linter() %}
+{%-   filter indent(8) %}
+# Install and run `rubocop`
+- gem install rubocop
+- rubocop -d
+{%-   endfilter %}
+{%- endmacro %}
+
+{%- set comment_linters = '# Run all of the linters in a single job' %}
+{%- set name_linters = 'Lint: salt-lint, yamllint, rubocop & commitlint' %}
+{%- if not travis.use_single_job_for_linters %}
+{%-   set comment_linters = comment_linters ~ ' (except `rubocop`)' %}
+{%-   set name_linters = 'Lint: salt-lint, yamllint & commitlint' %}
+{%- endif %}
 ## Machine config
 dist: {{ travis.dist }}
 {%- if platforms and not use_cirrus_ci %}
@@ -40,14 +65,15 @@ stages:
   - name: release
     if: branch = master AND type != pull_request
 jobs:
+  {{- format_allow_failures(travis.use_single_job_for_linters) }}
   include:
     ## Define the test stage that runs the linters (and testing matrix, if applicable)
 
-    # Run all of the linters in a single job
+    {{ comment_linters }}
     - language: node_js
       node_js: lts/*
       env: Lint
-      name: 'Lint: salt-lint, yamllint, rubocop & commitlint'
+      name: '{{ name_linters }}'
       before_install: skip
       script:
         # Install and run `salt-lint`
@@ -58,13 +84,24 @@ jobs:
         # Need at least `v1.17.0` for the `yaml-files` setting
         - pip install --user yamllint>=1.17.0
         - yamllint -s .
-        # Install and run `rubocop`
-        - gem install rubocop
-        - rubocop -d
+        {%- if travis.use_single_job_for_linters %}
+        {{-   format_rubocop_linter() }}
+        {%- endif %}
         # Install and run `commitlint`
         - npm install @commitlint/config-conventional -D
         - npm install @commitlint/travis-cli -D
         - commitlint-travis
+    {%- if not travis.use_single_job_for_linters %}
+    # Run the `rubocop` linter in a separate job that is allowed to fail
+    # Once these lint errors are fixed, this can be merged into a single job
+    - language: node_js
+      node_js: lts/*
+      env: Lint_rubocop
+      name: 'Lint: rubocop'
+      before_install: skip
+      script:
+        {{-   format_rubocop_linter() }}
+    {%- endif %}
 
     {%- if platforms and not use_cirrus_ci %}