Deleting a dataset in the webui with child snapshots

[subzero79]

The backend throws an error when zfs destroy(delete) pool/dataset exits non-zero if they are child snapshots.

Fix seems trivial, but should we:

1. add the -r switch to Dataset->destroy(), or

2. Catch the error if destroy exits non-zero

Comments?

[subzero79]

Sorry, forgot to mention. When this happens the mntent is also removed from database, that's the main problem

[artiomn]

I think if the error in child snapshots that can not be deleted without -r option, user should be asked with a dialog for deletion.