Update download-artifact to use zuul.artifacts

Also support the ability for child_jobs to fetch artifacts.

Change-Id: I0e2d43873410a095771503da712e67db5b64f25f
Signed-off-by: Paul Belanger <pabelanger@redhat.com>

roles/download-artifact/tasks/main.yaml

@@ -1,15 +1,33 @@
+---
+- name: Query inventory for artifact information
+  block:
+    - name: Parse inventory response
+      set_fact:
+        _artifacts: "{{ zuul.artifacts }}"
+  when: zuul.artifacts is defined
+
 - name: Query Zuul API for artifact information
-  uri:
-    url: "{{ download_artifact_api }}/builds?{{ download_artifact_query }}"
-  register: build
-- name: Parse build response
-  set_fact:
-    build: "{{ build.json[0] }}"
+  block:
+    - name: Fetch info from Zuul API
+      uri:
+        url: "{{ download_artifact_api }}/builds?{{ download_artifact_query }}"
+      register: build
+
+    - name: Parse build response
+      set_fact:
+        _artifacts: "{{ build.json[0].artifacts }}"
+  when: download_artifact_api is defined
+
+- name: Ensure artifacts directory exists
+  file:
+    path: "{{ download_artifact_directory }}"
+    state: directory
+
 - name: Download archive by type
   uri:
     url: "{{ artifact.url }}"
     dest: "{{ download_artifact_directory }}"
-  loop: "{{ build.artifacts }}"
+  loop: "{{ _artifacts }}"
   loop_control:
     loop_var: artifact
   when: "'metadata' in artifact and 'type' in artifact.metadata and (artifact.metadata.type == download_artifact_type or ((download_artifact_type | type_debug) == 'list' and artifact.metadata.type in download_artifact_type))"