Dead Share/Name Cleanup Issues

[michaelquigley]

Several users have gotten into a state where a share was killed without proper cleanup, making a name appear to be unavailable for sharing. Rather than zrok2 delete share and removing the share, the users did a zrok2 delete name... which got things into a broken state where the name is effectively unable to be used.

The fix is to make zrok2 delete share refuse to delete until referencing shares are properly disposed of.