[Proposal] Execute roles via roles static statement in play

[machacekondra]

Problem

This PR is just a proposal and open to discussion about the playbook structure. - We can execute roles from `roles:` statement in the play. - Use `pre_tasks` & `post_tasks` statements for the step file creation/deletion. - Use `vars` section to specify the tier.

This is just a possible way of doing the same thing with less verbose code.

[machacekondra]

@KimForss @rhmk please take a look.