Fix/misc bsdcan issues

[bellhyve]

Hi Richard,

Some fixes and minor improvements are ready for QA.

1. The stack of failover utilities is more resilient to protect from accidents and zfs allow or mount limitations: failover, lock, unlock, and propsync.
2. Prune's --visual output now labels each dataset rather than the run-on mess.
3. Prune's --visual now works with zprune; zprune keeps its usual output and functionality as well.
4. Prune Guard no longer blocks command output; it only blocks destructive actions in zprune.
5. zprune now emits a notice for --prune-size to remind the user that the size is applied per dataset, not shared across datasets (future feature).
6. Fixed --log-file="filename" handling; with --json, it prints regular output to standard error and clean JSON to the output file.

I also confirmed some docs and previous fixes. This shouldn't scramble the tests up too much except for the extra line of zprune output and the suppressed Zelta Guard warning.

Thanks!!!

Best,
Daniel