Fix role gate tests for Ansible 2.3

'ansible_become' defined as a host_var or in the inventory for a host
has a higher precedence than 'become' defined within a playbook.

In change Id5b76a87809f03951c954fc3d752419a673403f7, 'become' was
defined explicitly for each play running against localhost so
'ansible_become' should be removed from its host_vars.

Change-Id: I0a3019ed7f4e151625682d009e5359378152592d

tests/host_vars/localhost.yml

@@ -13,7 +13,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-ansible_become: True
 neutron_local_ip:  10.1.2.1
 ansible_python_interpreter: "/usr/bin/python2"
 bridges:

tests/test-ironic-cli.yml

@@ -16,6 +16,7 @@
 - name: Test the ironic CLI
   hosts: hosts
   user: root
+  become: true
   gather_facts: false
   tasks:
     - name: Run the ironic chassis-list command

tests/test-rest-api.yml

@@ -2,6 +2,7 @@
 - name: Playbook for functional testing ironic via its REST API
   hosts: localhost
   user: root
+  become: true
   gather_facts: true
   roles:
     - role: "openstack_openrc"