Make upload_file robust against failures of all kinds, in particular it now handles failures of complete_upload (I've seen these in the wild).  Also, in put_from_manifest, don't delete backup sstables if they failed to upload (as, unlike snapshots, you can't get them back after deleting them).
Make upload_file robust against failures of all kinds, in particular it now
handles failures of complete_upload (I've seen these in the wild).  Also, in
put_from_manifest, don't delete backup sstables if they failed to upload (as,
unlike snapshots, you can't get them back after deleting them).

merlin83/cassandra_snapshotter