Support for basic authentication access

[janhoy]

SOLR-4470 adds support for basic auth credentials and thus ability to lock down a whole SolrCloud cluster without firewalling.

We already have HTTPS support built in to tomcat config with certificates, but it won't work with Solr until 4470 is solved, and we also need to support basic auth.

If 4470 drags out, consider adding it as a patch, once issue #5 is solved