Move fedora_content_location inside io hash for export script

[bbarberBPL]

Move the fedora_content_location attribute inside a an attribute called io which should be a hash in Bplmodels::DatastreamExport in the files_for_export method
Ex.

file_hash = { ...
io: 
   { fedora_content_location: 'http://url_to_fedora_location }
}