This patch includes three unrelated fixes.

Make qemu use nova user in centos
Libvirt 3.2.0 (latest version in centos) seems to
have changed behavior of dynamic_ownership.

Pin ansible to <2.4 to make ara work in gates
ARA does not work yet with ansible 2.4, this change
pins to lower version to make gates work.
Revert once ara works with 2.4

Disable selinux for oraclelinux and centos.

Co-Authored-By: wanghongxu <wang19930902@gmail.com>
Co-Authored-By: Jeffrey Zhang <jeffrey.zhang@99cloud.net>
Change-Id: Iac8bec19437192cd198d58f71c6ed0a65a76f820
Closes-bug: #1718541