Multiple sites (mutlisite) in the same index

[VeggieMeat]

Original issue: https://www.drupal.org/node/2462445

Posting a patch to allow for multiple sites to be stored in the same index. This patch requires that this sandbox module to be enabled: https://www.drupal.org/sandbox/e2thex/2033065. That sandbox module adds a site hash filter (a field in the elastic index) and this patch allows it to be used for elastic search. So, multiple sites can be stored in the same index without deleting each other's content and a filter can be used in views that will allow searching across all sites in the index or only the current site.