Investigate indexing OSDF origins using pelicanfs

Currently OSDF origins are indexed by looking through CVMFS. This presents unnecessary requirements on the GWDataFind server host, and also adds a reliance on CVMFS that should be removed.

#40 (closed) proposes enabling talking to remote diskcache instances, which would enable moving the diskcache onto the OSDF origin itself.

An alternative solution might be to index OSDF origins dynamically over HTTP using the pelicanfs client.