scripts using curl should support authentication params

All scripts that utilize "curl" should be enhanced such that user authentication based params can be specified and used by curl. This would make it possible for people to "secure" their Solr servers using Servlet Container authentication features, but still interact with those Solr instances using the scripts out of the box.

The most straight forward approach would probably be to add a new "curl_args" option in scripts.conf that could could contain any legal curl command line options and would be prepended to the args for all usages of curl in the Solr scripts.