Make tempest log to be written to reports directory

Change-Id: Idab4de95f4b307b7e697fd2cc7aab8f85903c38c
Related-Prod: 17348
(cherry picked from commit 3754fd85f5f7ab5b65f4b7c1d8d213f5eae251e4)
diff --git a/classes/cluster/virtual-mcp11-aio/openstack/init.yml b/classes/cluster/virtual-mcp11-aio/openstack/init.yml
index beada77..bb8a80a 100755
--- a/classes/cluster/virtual-mcp11-aio/openstack/init.yml
+++ b/classes/cluster/virtual-mcp11-aio/openstack/init.yml
@@ -123,6 +123,8 @@
       enabled: True
       cfg_dir: ${_param:runtest_tempest_cfg_dir}
       cfg_name: ${_param:runtest_tempest_cfg_name}
+      DEFAULT:
+        log_file: /home/rally/rally_reports/tempest.log
       compute:
         build_timeout: 600
         min_microversion: 2.1