Changes for Ansible 2.4

Squashed changes:
   - Use 'inventory' instead of 'hostfile' in ansible.cfg.

     'hostfile' is deprecated.

   - Use 'os.environ.copy()' in zuul_return.py since this causes 2.4 to
     throw an exception now deep within module.exit_json().

Change-Id: I0a52c9e169a54d24a7b361010045fb10211418b7

tools/test-logs.sh

@@ -42,7 +42,7 @@ fi
 
 cat >$WORK_DIR/ansible.cfg <<EOF
 [defaults]
-hostfile = $INVENTORY
+inventory = $INVENTORY
 gathering = smart
 gather_subset = !all
 fact_caching = jsonfile