This method is currently used in two places: sstable::snapshot() and
sstable::seal_sstable(). The latter additionally touches the target
backup/ subdir.
This patch moves the whole thing on storage and adds touch for all the
cases. For snapshots this might be excessive, but harmless.
Tests get their private-disclosure way to access sstable._storage in
few places to call create_links directly.
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
18f6165993