Fix "none" traceback when editing dataset

Error: concurrent.futures.process._RemoteTraceback:
"""
Traceback (most recent call last):
  File "/usr/local/lib/python3.6/site-packages/middlewared/plugins/zfs.py", line 327, in do_update
    dataset.properties[k] = prop
  File "libzfs.pyx", line 374, in libzfs.ZFS.__exit__
  File "/usr/local/lib/python3.6/site-packages/middlewared/plugins/zfs.py", line 316, in do_update
    prop.value = v['value']
  File "libzfs.pyx", line 1069, in libzfs.ZFSProperty.value.__set__
libzfs.ZFSException: use 'none' to disable quota/refquota

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/local/lib/python3.6/concurrent/futures/process.py", line 175, in _process_worker
    r = call_item.fn(*call_item.args, **call_item.kwargs)
  File "/usr/local/lib/python3.6/site-packages/middlewared/worker.py", line 131, in main_worker
    res = loop.run_until_complete(coro)
  File "/usr/local/lib/python3.6/asyncio/base_events.py", line 468, in run_until_complete
    return future.result()
  File "/usr/local/lib/python3.6/site-packages/middlewared/worker.py", line 91, in _run
    return await self._call(name, serviceobj, methodobj, params=args, job=job)
  File "/usr/local/lib/python3.6/site-packages/middlewared/worker.py", line 84, in _call
    return methodobj(*params)
  File "/usr/local/lib/python3.6/site-packages/middlewared/worker.py", line 82, in _call
    return await methodobj(*params)
  File "/usr/local/lib/python3.6/site-packages/middlewared/service.py", line 295, in update
    f'{self._config.namespace}.update', self, self.do_update, [id, data]
  File "/usr/local/lib/python3.6/site-packages/middlewared/worker.py", line 84, in _call
    return methodobj(*params)
  File "/usr/local/lib/python3.6/site-packages/middlewared/worker.py", line 84, in _call
    return methodobj(*params)
  File "/usr/local/lib/python3.6/site-packages/middlewared/schema.py", line 668, in nf
    return f(*args, **kwargs)
  File "/usr/local/lib/python3.6/site-packages/middlewared/plugins/zfs.py", line 331, in do_update
    raise CallError(f'Failed to update dataset: {e}')
middlewared.service_exception.CallError: [EFAULT] Failed to update dataset: use 'none' to disable quota/refquota
"""

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/usr/local/lib/python3.6/site-packages/middlewared/main.py", line 166, in call_method
    result = await self.middleware.call_method(self, message)
  File "/usr/local/lib/python3.6/site-packages/middlewared/main.py", line 1097, in call_method
    return await self._call(message['method'], serviceobj, methodobj, params, app=app, io_thread=False)
  File "/usr/local/lib/python3.6/site-packages/middlewared/main.py", line 1045, in _call
    return await methodobj(*args)
  File "/usr/local/lib/python3.6/site-packages/middlewared/service.py", line 295, in update
    f'{self._config.namespace}.update', self, self.do_update, [id, data]
  File "/usr/local/lib/python3.6/site-packages/middlewared/main.py", line 1045, in _call
    return await methodobj(*args)
  File "/usr/local/lib/python3.6/site-packages/middlewared/schema.py", line 664, in nf
    return await f(*args, **kwargs)
  File "/usr/local/lib/python3.6/site-packages/middlewared/plugins/pool.py", line 757, in do_update
    rv = await self.middleware.call('zfs.dataset.update', id, {'properties': props})
  File "/usr/local/lib/python3.6/site-packages/middlewared/main.py", line 1101, in call
    return await self._call(name, serviceobj, methodobj, params, app=app, pipes=pipes, io_thread=True)
  File "/usr/local/lib/python3.6/site-packages/middlewared/main.py", line 1042, in _call
    return await self._call_worker(name, *args)
  File "/usr/local/lib/python3.6/site-packages/middlewared/main.py", line 1062, in _call_worker
    return await self.run_in_proc(main_worker, name, args, job)
  File "/usr/local/lib/python3.6/site-packages/middlewared/main.py", line 996, in run_in_proc
    return await self.run_in_executor(self.__procpool, method, *args, **kwargs)
  File "/usr/local/lib/python3.6/site-packages/middlewared/main.py", line 972, in run_in_executor
    return await loop.run_in_executor(pool, functools.partial(method, *args, **kwargs))
middlewared.service_exception.CallError: [EFAULT] Failed to update dataset: use 'none' to disable quota/refquota