When executing the deployment_steps_playbook.yaml passing
a specific --tags, it looks like this play gets executed
even though the tag passed in --tags isn't common_roles.
This patch converts the roles: structure into a:
which is the prefered way since Ansible 2.4. This way, the
tags work properly and the execution of both roles is skipped
if the tag doesn't match common_roles.
(cherry picked from commit