MEMO-780: Search for sftp locators in all instantiations

Previously the RdfHandler only searched for locators starting with
the string "sftp:" in RDF resources of RICO type "digitalObject",
which resulted in binaries for thumbnails not being ingested into
fedora. This commit fixes this bug by searching for locators that
point to the sftp server in all instantiatons.
4 jobs for 0.6.12 in 4 minutes and 3 seconds (queued for 2 seconds)