Fix role gate tests for Ansible 2.3

Add 'become' and root 'user' options to the playbook instead of using
'ansible_become' through an inventory variable.

Change-Id: I5a3e9d20a577209f3181054a5ee3ea84de1d1a39

tests/inventory

@@ -1,5 +1,5 @@
 [all]
-localhost ansible_connection=local ansible_become=True
+localhost
 
 [haproxy_all]
 localhost

tests/test.yml

@@ -16,6 +16,8 @@
 - name: Playbook for role testing
   hosts: localhost
   connection: local
+  user: root
+  become: true
   roles:
     - role: "haproxy_server"
   vars_files: