Missing kerberos support in curator

xpack can handle kerberos authentication and many [others](https://www.elastic.co/guide/en/cloud/current/ec-security.html)

None of them are allowed in curator.

When providing kerberos support, please don' forget about keytab files handling.

Start by tracing Curator’s authentication configuration and Elasticsearch client setup, then compare the linked xpack authentication capabilities. Define how Kerberos credentials and keytab files should be configured and handled; done means Curator accepts Kerberos authentication consistently with the requested xpack support.

Written by the indexing model from the issue text.