Updated repository root RDF to use standard vocabulary sd:endpoint to point at the fcr:sparql service.

https://www.pivotaltracker.com/s/projects/684825/stories/72619838
The root rdf output will be changed to use the sd:endpoint as follows now:
<rdf:Description rdf:about="http://localhost:8080/rest/">
<endpoint xmlns="http://www.w3.org/ns/sparql-service-description#" rdf:resource="http://localhost:8080/rest/fcr:sparql"/>
...
</rdf:Description>
Why did you add the sd namespace to this file?