Don't create a gzipped folder: recursively gzip ARA contents

https://review.openstack.org/#/c/495551/ introduced gzipping through
the "archive" module but the result isn't the expected one, let's use
the gzip command instead.

Change-Id: I7d5fe19381ade6639ec4d96b50e58f84439e0230

roles/emit-ara-html/tasks/main.yaml

@@ -14,6 +14,5 @@
   when: ara_command_type|succeeded and not ara_command_type|skipped
 
 - name: Compress ARA html output
-  archive:
-    path: "{{ zuul.executor.log_root }}/ara"
+  command: gzip --recursive --best {{ zuul.executor.log_root }}/ara
   when: ara_compress_html | bool