Asset filter results no longer retrieve site ID

[gschneider-r7]

I believe this is due to changes in Nexpose 5.13.0, which enabled global asset linking. The results of the filter search now present the site ID differently. Need to update how the site_id is obtained.

It looks like we need to traverse the sitePermissions array in the JSON response to get multiple siteIDs. The JSON does not indicate which site is "primary". If we provide an array of site_ids then this will be a backwards-incompatible change to the gem.