Remove tempest_image_dir_owner var

tempest_image_dir_owner is used to create tempest_image_dir.
and sets proper directory permission, user and group.
Let's use default ansible user to create the directory instead
of restricting on tempest_image_dir_owner user.

Change-Id: I4ccad998f2b9ef84dbe7f645f31960b38c6fd27a

defaults/main.yml

@@ -240,7 +240,6 @@ tempest_images:
 
 # The location where images are downloaded to
 tempest_image_dir: "/opt/cache/files"
-tempest_image_dir_owner: "{{ lookup('env', 'USER') }}"
 
 tempest_enable_instance_password: True
 

releasenotes/notes/remove-tempest-image-dir-owner-ec10dfa5bb9f87f1.yaml

@@ -0,0 +1,5 @@
+---
+upgrade:
+  - The variable ``tempest_image_dir_owner`` is removed in
+    favour of using default ansible user to create the
+    image directory.

tasks/tempest_resources.yml

@@ -34,10 +34,6 @@
       file:
         path: "{{ tempest_image_dir }}"
         state: directory
-        mode: "0750"
-        owner: "{{ tempest_image_dir_owner }}"
-        recurse: yes
-      become: yes
       when:
         - tempest_service_available_glance | bool