zfs: fix incompatibility - share.nfs vs sharenfs (issue #7696)

Implement the fix proposed on the [ticket](https://github.com/ansible/ansible/issues/7696).

Note that zfs itself accepts "sharenfs" as an alias for "share.nfs", so there is no problem setting the property. The new name only causes issues because we dump all properties to a dict and then expect it to contain "sharenfs".