attributes/cloud_monitoring.rb blows up if cloud monitoring toggle is turned off

There's `can't convert nil into String` when we turn off cloud monitoring using `node['platformstack']'cloud_monitoring']['enabled']=false`, due to this in attributes/cloud_monitoring.rb:
```
        50:  node['filesystem'].each do |key, data|
        51>>   next if data['percent_used'].nil? || default['platformstack']['cloud_monitoring']['filesystem']['non_monitored_fstypes'].include?(data['fs_type'])
        52:    default['platformstack']['cloud_monitoring']['filesystem']['target'][key] = data['mount']
        53:  end
```