[doc] Add firewall configuration step of quickstart guide
[doc] Add firewall configuration step of quickstart guide

The firewalld service should be masked during configuring the OS.

Change-Id: I08ef6a39ed245195aafe9db8d7339c0b1044374f
Closes-Bug: #1848082

stackforge/os-ansible-deployment,stackforge/os-ansible-deployment,openstack/openstack-ansible,openstack/openstack-ansible