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: I7eb8275699d418848b0991c5ba232ae0b9ffb42e

tests/inventory

@@ -1,2 +1,2 @@
 [all]
-localhost ansible_connection=local ansible_become=True
+localhost

tests/test.yml

@@ -16,5 +16,7 @@
 - name: Playbook for role testing
   hosts: localhost
   connection: local
+  user: root
+  become: true
   roles:
     - role: "ceph_client"