Elastic: regenerate picture URL before inserting into ElasticSearch

This ensures the thumbnail URL is public so that it won't expire.
Since this now requires API calls to Google, I've increased the number of
parallel threads used for indexing, since they'll be waiting for network
I/O more.

pillar/cli/elastic.py

@@ -17,7 +17,7 @@ name_to_task = {
     'nodes': index.ResetNodeIndex,
     'users': index.ResetUserIndex,
 }
-REINDEX_THREAD_COUNT = 3
+REINDEX_THREAD_COUNT = 5
 
 
 @manager_elastic.option('indices', nargs='*')