Allow download-artifact to download multiple files

In order to support downloading artifacts from a python build job,
which mayb produce multiple sdist tarballs and wheels, allow this
role to download as many files as match the input parameters.

Change-Id: I59de60127b1e8499ae3e48f2a1bc56c7a36b7425

roles/download-artifact/README.rst

@@ -1,7 +1,8 @@
-Download an artifact from a completed build of a Zuul job
+Download artifacts from a completed build of a Zuul job
 
-Given a change downloads an artifact from a previous build (by default
-of the current change) into the work directory.
+Given a change, downloads artifacts from a previous build (by default
+of the current change) into the work directory.  This will download as
+many artifacts as match the selection criteria.
 
 **Role Variables**
 
@@ -19,10 +20,14 @@ of the current change) into the work directory.
 
 .. zuul:rolevar:: download_artifact_name
 
-   The artifact name.
+   The artifact name.  This can be a string or a list of strings.
 
 .. zuul:rolevar:: download_artifact_query
    :default: change={{ zuul.change }}&patchset={{ zuul.patchset }}&pipeline={{ download_artifact_pipeline }}&job_name={{ download_artifact_job }}
 
-   The query to use to find the build.  This should return exactly one
-   result.  Normally the default is used.
+   The query to use to find the build.  Normally the default is used.
+
+.. zuul:rolevar:: download_artifact_directory
+   :default: {{ zuul.executor.work_root }}
+
+   The directory in which to place the downloaded artifacts.

roles/download-artifact/defaults/main.yaml

@@ -1,2 +1,3 @@
 ---
 download_artifact_query: "change={{ zuul.change }}&patchset={{ zuul.patchset }}&pipeline={{ download_artifact_pipeline }}&job_name={{ download_artifact_job }}"
+download_artifact_directory: "{{ zuul.executor.work_root }}"

roles/download-artifact/tasks/inner.yaml

@@ -0,0 +1,8 @@
+- name: Download archive
+  uri:
+    url: "{{ artifact.url }}"
+    dest: "{{ download_artifact_directory }}"
+  loop: "{{ (build.artifacts }}"
+  loop_control:
+    loop_var: artifact
+  when: "artifact.name == download_artifact_name or ((download_artifact_name | type_debug) == 'list' and artifact.name in download_artifact_name)"

roles/download-artifact/tasks/main.yaml

@@ -5,7 +5,8 @@
 - name: Extract artifact URL
   set_fact:
     archive_url: "{{ (build.json[0].artifacts | selectattr('name', 'equalto', download_artifact_name) | list)[0].url }}"
-- name: Download archive
-  uri:
-    url: "{{ archive_url }}"
-    dest: "{{ zuul.executor.work_root }}"
+- name: Process build
+  loop: "{{ build.json }}"
+  loop_control:
+    loop_var: build
+  include_tasks: inner.yaml