[Scylla Node]: move the logic away from io_properties.yaml.j2

[vladzcloudius]

HEAD: 1b1a487

Description

io_properties.yaml.j2 has the following business logic code today:

{% if scylla_io_probe|bool and scylla_io_probe_dc_aware|bool %}
{{ hostvars[dc_to_node_list[dc][0]]['io_properties'] | to_yaml }}
{% else %}
...

This is rather unnatural because the code reader wouldn't think to look for parts of a non-trivial logic in JINJA which is supposed to be a trivial template.

We should move this code outside to the Ansible code.