tests/functional: Use the ansible reboot module
tests/functional: Use the ansible reboot module

Ansible 2.7 introduces the reboot module so we don't need to use the
shell/reboot + wait_for tasks.

https://docs.ansible.com/ansible/latest/modules/reboot_module.html

Signed-off-by: Dimitri Savineau <a50a620e679eed14f4e99998b821cea8884cf228@redhat.com>

ceph/ceph-ansible,ceph/ceph-ansible