Rename the 'neutron-policy-overrides' tag to 'neutron-policy-override'
so that it's consistent with the other tagged task in this role and all
other openstack-ansible service roles.
Change-Id: I7af67908920bf386d204e28cbf5b936fea76ecd0
(cherry picked from commit e9db0fce111828695ce190106e5d0c3eef587410)