Ensure destination exists when using SSH storage

internal/storage/ssh/ssh.go

@@ -107,6 +107,10 @@
 
 // Copy copies the given file to the SSH storage backend.
 func (b *sshStorage) Copy(file string) (returnErr error) {
+	if err := b.sftpClient.MkdirAll(b.DestinationPath); err != nil {
+		return errwrap.Wrap(err, "error ensuring destination directory")
+	}
+
 	source, err := os.Open(file)
 	_, name := path.Split(file)
 	if err != nil {
@@ -170,6 +174,10 @@
 func (b *sshStorage) Prune(deadline time.Time, pruningPrefix string) (*storage.PruneStats, error) {
 	candidates, err := b.sftpClient.ReadDir(b.DestinationPath)
 	if err != nil {
+		// If directory doesn't exist yet, nothing to prune
+		if errors.Is(err, os.ErrNotExist) {
+			return &storage.PruneStats{}, nil
+		}
 		return nil, errwrap.Wrap(err, "error reading directory")
 	}