test-upload-logs-swift: fix download link

We can just find the basename of the template file, and return that --
the artifact will be a relative URL which will be right.

For additional help, add a metadata string you could copy-paste to
download.

Change-Id: I1a6f931fdd1613d1e51a20ed76a69c76bbb14dc1

roles/test-upload-logs-swift/tasks/main.yaml

@@ -37,13 +37,21 @@
         download_template: "{{ download_template | default(omit) }}"
       register: upload_results
 
+    - name: Get download script name
+      set_fact:
+        download_script: "{{ zuul_log_download_template | basename | regex_replace('\\.j2$') }}"
+      when:
+        - zuul_log_include_download_script
+
     - name: Set download template artifact
       zuul_return:
         data:
           zuul:
             artifacts:
-              - name: bulk-download
-                url: '{{ upload_results.url }}/{{ zuul_log_download_template[:-3] }}'
+              - name: Download all logs
+                url: '{{ download_script }}'
+                metadata:
+                  command: 'curl "{{ upload_results.url }}/{{ download_script }}" | bash'
       when:
         - zuul_log_include_download_script