Use roundtrip context manager in distributed write tests

[dcherian]

What is your issue?

File roundtripping tests in test_distributed.py don't use the roundtrip context manager (thpugh one uses create_tmp_file) so I don't think any created files are being cleaned up.

Example:

xarray/xarray/tests/test_distributed.py

Lines 91 to 119 in 09e467a

	def test_dask_distributed_netcdf_roundtrip(
	loop, tmp_netcdf_filename, engine, nc_format
	):
	if engine not in ENGINES:
	pytest.skip("engine not available")
	chunks = {"dim1": 4, "dim2": 3, "dim3": 6}
	with cluster() as (s, [a, b]):
	with Client(s["address"], loop=loop):
	original = create_test_data().chunk(chunks)
	if engine == "scipy":
	with pytest.raises(NotImplementedError):
	original.to_netcdf(
	tmp_netcdf_filename, engine=engine, format=nc_format
	)
	return
	original.to_netcdf(tmp_netcdf_filename, engine=engine, format=nc_format)
	with xr.open_dataset(
	tmp_netcdf_filename, chunks=chunks, engine=engine
	) as restored:
	assert isinstance(restored.var1.data, da.Array)
	computed = restored.compute()
	assert_allclose(original, computed)