GLUE2: add GLUE2EndpointImplementation information

The EGI GLUE2 profile requires us to publish the implementation name
and version for all published endpoints, which we currently don't
do.

This patch adds this information.

Target: master
Request: 2.6
Request: 2.2
Patch: http://rb.dcache.org/r/5591/
Acked-by: Gerd Behrmann