Add role for fetching javascript built content

Built content and source tarballs are different. Have a role that
handles uploading built content.

Append -content to the tarball so that a project can publish both a
source tarball and a built content tarball without stepping on each
other.

Change-Id: I33dff8080018bda281a00e648468de80d3ecd679

roles/fetch-javascript-content-tarball/README.rst

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+Fetch a Javascript content tarball back to be published.
+
+A content tarball is one that contains built javascript/css artifacts,
+such as but not limited to those produced by the webpack ArchivePlugin.
+
+**Role Variables**
+
+.. zuul:rolevar:: zuul_work_dir
+   :default: {{ zuul.project.src_dir }}
+
+   Directory to work in.

roles/fetch-javascript-content-tarball/defaults/main.yaml

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+zuul_work_dir: "{{ zuul.project.src_dir }}"

roles/fetch-javascript-content-tarball/tasks/main.yaml

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+- name: Rename tarball for uploading
+  shell: |
+    mkdir -p dist
+    cp *.tgz dist/{{ zuul.project.short_name }}-content-latest.tar.gz
+  args:
+    chdir: "{{ zuul_work_dir }}"
+  tags:
+    # Ignore ANSIBLE0007: No need to use file module instead of mkdir
+    - skip_ansible_lint
+
+- name: Rename tagged tarball for uploading
+  when: zuul.tag is defined
+  shell: |
+    cp *.tgz dist/{{ zuul.project.short_name }}-content-{{ zuul.tag }}.tar.gz
+  args:
+    chdir: "{{ zuul_work_dir }}"
+
+- name: Ensure artifacts directory exists
+  file:
+    path: "{{ zuul.executor.work_root }}/artifacts"
+    state: directory
+  delegate_to: localhost
+
+- name: Collect artifacts
+  synchronize:
+    dest: "{{ zuul.executor.work_root }}/artifacts/"
+    mode: pull
+    src: "{{ zuul_work_dir }}/dist/"
+    verify_host: true