Enable serial execution for ansible host
Enable serial execution for ansible host

Allow to override serial parameter for parallel execution
in Ansible

Needed-By: Iafd7c58aaf2f1b30cf46cd16122b5821c96c497c
Needed-By: I15511b4f36260292e0ea4100b15b8e65a701b38b

Change-Id: I707282bf3cfcc7e370af41f987700e39c1b0b268

openstack/tripleo-heat-templates,openstack/tripleo-heat-templates