Allow rethinkdb input plugin to work with RethinkDB 2.3.5+ databases that requires username,password authorization and Handshake protocol v1.0

* remove top level header not required in sample config

* remove top level header not required in sample config

fixes #2934

Parsing dos line ending delimited line protocol is still illegal in most
cases.

This was broken by changes in go 1.8 to url.Parse.  This change allows
the string but prompts the user to move to the correct url string.