Add role to fetch output from nodes

When jobs put their output into output dirs, it needs to be fetched back
to the executors for publication.

Change-Id: I3dfbbd4327102b62160713ca782dfa4b13d26924

roles/fetch-output/README.rst

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+Collect output from build nodes
+
+This role collects logs, artifacts and docs from subdirs of the
+``zuul_output_dir`` on the remote nodes to equivalent directories
+on the executor so that later parts of the system can publish the
+content to appropriate permanent locations.
+
+**Role Variables**
+
+.. zuul:rolevar:: zuul_output_dir
+   :default: {{ ansible_user_dir }}/zuul-output
+
+   Base directory for collecting job output.

roles/fetch-output/defaults/main.yaml

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+zuul_output_dir: "{{ ansible_user_dir }}/zuul-output"

roles/fetch-output/tasks/main.yaml

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+- name: Set log path for multiple nodes
+  set_fact:
+    log_path: "{{ zuul.executor.log_root }}/{{ inventory_hostname }}"
+  when: groups['all'] | length > 1
+
+- name: Set log path for single node
+  set_fact:
+    log_path: "{{ zuul.executor.log_root }}"
+  when: log_path is not defined
+
+- name: Ensure local output dirs
+  file:
+    path: "{{ item }}"
+    state: directory
+  with_items:
+    - "{{ log_path }}"
+    - "{{ zuul.executor.work_dir }}/artifacts"
+    - "{{ zuul.executor.work_dir }}/docs"
+
+- name: Collect log output
+  synchronize:
+    dest: "{{ log_path }}/"
+    mode: pull
+    src: "{{ zuul_output_dir }}/logs/"
+    verify_host: true
+
+- name: Collect artifacts
+  synchronize:
+    dest: "{{ zuul.executor.work_dir }}/artifacts/"
+    mode: pull
+    src: "{{ zuul_output_dir }}/artifacts/"
+    verify_host: true
+
+- name: Collect docs
+  synchronize:
+    dest: "{{ zuul.executor.work_dir }}/docs/"
+    mode: pull
+    src: "{{ zuul_output_dir }}/docs/"
+    verify_host: true