config: look up for monitor_address_block in hostvars

config: look up for monitor_address_block in hostvars

`monitor_address_block` should be read from hostvars[host] instead of
current node being played.

eg:

Let's assume we have:

```
[mons]
ceph-mon0 monitor_address=192.168.1.10
ceph-mon1 monitor_interface=eth1
ceph-mon2 monitor_address_block=192.168.1.0/24
```

the ceph.conf generation task will end up with:

```
fatal: [ceph-mon0]: FAILED! => {}

MSG:

'ansible.vars.hostvars.HostVarsVars object' has no attribute u'ansible_interface'
```

the reason is that it will assume `monitor_address_block` isn't defined even on
ceph-mon2 because looking for `monitor_address_block` instead of
`hostvars[host]['monitor_address_block']`, therefore it enters in the condition as default value:

```
    {%- else -%}
      {% set interface = 'ansible_' + (monitor_interface | replace('-', '_')) %}
      {% if ip_version == 'ipv4' -%}
        {{ hostvars[host][interface][ip_version]['address'] }}
      {%- elif ip_version == 'ipv6' -%}
        [{{ hostvars[host][interface][ip_version][0]['address'] }}]
      {%- endif %}
    {%- endif %}
```

`monitor_interface` is set with default value `'interface'` so the `interface`
variable is built with 'ansible_' + 'interface'. It makes ansible throwing a
confusing message about `'ansible_interface'`.

Closes: https://bugzilla.redhat.com/show_bug.cgi?id=1635303
Signed-off-by: Guillaume Abrioux <gabrioux@redhat.com>