Improve performance of check for usable storage
Improve performance of check for usable storage

By checking if asset is not present in the NFS first will speed things
up for newly created assets and the ones fully migrated to S3 and no
longer in the NFS.

Eventually all assets will be permanently in S3 and checking NFS is
theoretically faster than S3 since the latter involves an HTTP call.

powerhome/paperclip-eitheror