In58784cd,aa4b06aand other commits migrating hinted handoff from IPs to host IDs (scylladb/scylladb#15567), we started ignoring hint directories of invalid names, i.e. those that represent neither an IP address, nor a host ID. They remain on disk and are taken into account while computing e.g. the total size of hints, but they're not used in any way. These changes add logs informing the user when Scylla encounters such a directory. Closes scylladb/scylladb#17566