iscsi: fix permission denied error

iscsi: fix permission denied error

Typical error:
```
fatal: [iscsi-gw0]: FAILED! =>
  msg: 'an error occurred while trying to read the file ''/home/guits/ceph-ansible/tests/functional/all_daemons/fetch/e5f4ab94-c099-4781-b592-dbd440a9d6f3/iscsi-gateway.key'': [Errno 13] Permission denied: b''/home/guits/ceph-ansible/tests/functional/all_daemons/fetch/e5f4ab94-c099-4781-b592-dbd440a9d6f3/iscsi-gateway.key'''
```

`become: True` is not needed on the following task:

`copy crt file(s) to gateway nodes`.

Since it's already set in the main playbook (site.yml/site-container.yml)

The thing is that the files get generated in the 'fetch_directory' with
root user because there is a 'delegate_to' + we run the playbook with
`become: True` (from main playbook).

The idea here is to create files under ansible user so we can open them
later to copy them on the remote machine.

Signed-off-by: Guillaume Abrioux <gabrioux@redhat.com>
(cherry picked from commit 9d590f4339a4d758f07388bf97b7eabdcbca6043)