* Fix bootstrap_os/ubuntu idempotency

* Update bastion role

* move container_engine in sub-roles

* requires ansible 2.5

* ubuntu18 as first CI job

This will allow running Kubespray when the user who runs it doesn't
have write permissions to the Kubespray dir, at least when not using
bastion.

* Changre raw execution to use yum module

Changed raw exection to use yum module provided by Ansible.

* Replace ansible_ssh_* by ansible_*

Ansible 2.0 has deprecated the “ssh” from ansible_ssh_user, ansible_ssh_host, and ansible_ssh_port to become ansible_user, ansible_host, and ansible_port. If you are using a version of Ansible prior to 2.0, you should continue using the older style variables (ansible_ssh_*). These shorter variables are ignored, without warning, in older versions of Ansible.

I am not sure about the broader impact of this change. But I have seen on the requirements the version required is ansible>=2.4.0.

http://docs.ansible.com/ansible/latest/intro_inventory.html

* Added private key file to ssh bastion conf

* Used regular if condition insted of inline conditional

Migrate older inline= syntax to pure yml syntax for module args as to be consistant with most of the rest of the tasks
Cleanup some spacing in various files
Rename some files named yaml to yml for consistancy

'absible_ssh_host' is deprecated in Ansible 2.0 and at least
'contrib/inventory_builder/inventory.py' uses 'ansible_host' instead.