Forcing to avoid the use of become on locally delegated tasks

[tiraboschi]

locally delegated tasks.

The whole role can be also executed with
delegate_to: root as a regular
user on the ansible controller node.

Cleaning up .ssh/know_hosts for
leftovers on the ansible controller
should happen as current user also in that case.

Fixes: #143

[tiraboschi]

Fixes https://bugzilla.redhat.com/1693607

[tiraboschi]

Verified deploying over a remote host as an unprivileged user with sudo right on the target host:

[stirabos@ansiblec ~]$ ansible-playbook -i c76he20190321h1.localdomain, hosted_engine_deploy.yml --extra-vars='@he_deployment.json' --extra-vars='@passwords.yml' --ask-vault-pass
...
PLAY RECAP *******************************************************************************************************************************************************************************************************************************************************************************
c76he20190321h1.localdomain : ok=352  changed=120  unreachable=0    failed=0   

[stirabos@ansiblec ~]$ cat hosted_engine_deploy.yml 
---
- name: Deploy oVirt hosted engine
  hosts: c76he20190321h1.localdomain
  become: true
  become_user: root
  roles:
    - role: ovirt.hosted_engine_setup