ceph-rgw: Make sure pool name templates are expanded

ceph-rgw: Make sure pool name templates are expanded

It is common to set templated pool names in `rgw_create_pools`, e.g.

```yaml
rgw_create_pools:
  "{{ rgw_zone }}.rgw.buckets.index":
    pg_num: 16
    size: 3
    type: replicated
```

This worked fine with Ansible 2.8, but broke in Ansible 2.9 due to a change in
the way `with_dict` works [1].

This commit replaces the use of `with_dict` with

```yaml
loop: "{{ rgw_create_pools | dict2items }}"
```

which works as intended and expands the template in the pool name.

[1]: https://docs.ansible.com/ansible/latest/porting_guides/porting_guide_2.9.html#loops

Closes #5348

Signed-off-by: Benoît Knecht <bknecht@protonmail.ch>