shorten snapshot paths to fit 88 char limit in iocage jails

[rpepr]

FreeBSD has a long standing limitation that mount paths be 88 characters or less. With adlbre-backup running inside an iocage jail this limit makes the zfs snapshots unmountable since the mount path for the jail adds at least 27 characters to the path. I got around this by giving snapshots 2 digit numeric names and renaming hosts to h. The original snapshot name is stored in l/snap_data.

A side benefit of this change is that the zfs mountpoint can differ from the dataset name. My data set has a longish name to fit my convention for jailed data. It gets mounted on /b.

The changes are activated by HACK88=1 in backup.conf.

RP

[macropin]

Thanks for this. I don't think we're going to merge this right now. But I'll leave it open in case someone else finds it useful.