id,node_id,number,title,user,state,locked,assignee,milestone,comments,created_at,updated_at,closed_at,author_association,active_lock_reason,draft,pull_request,body,reactions,performed_via_github_app,state_reason,repo,type
528154893,MDU6SXNzdWU1MjgxNTQ4OTM=,3572,Context manager `AttributeError` when engine='h5netcdf',500246,closed,0,,,2,2019-11-25T15:19:29Z,2019-11-25T16:12:37Z,2019-11-25T16:12:37Z,CONTRIBUTOR,,,,"Opening this NetCDF file works fine with the default engine, but fails with AttributeError with the h5netcdf engine:

#### MCVE Code Sample

Data available from EUMETSAT: https://www.eumetsat.int/website/home/Satellites/FutureSatellites/MeteosatThirdGeneration/MTGData/MTGUserTestData/index.html  --> ftp://ftp.eumetsat.int/pub/OPS/out/test-data/Test-data-for-External-Users/MTG_FCI_Test-Data/ --> uncompressed

```python

import xarray
f = ""/path/to/.../W_XX-EUMETSAT-Darmstadt,IMG+SAT,MTI1+FCI-1C-RRAD-FDHSI-FD--CHK-BODY--L2P-NC4E_C_EUMT_20170410114434_GTT_DEV_20170410113925_20170410113934_N__C_0070_0067.nc""
ds = xarray.open_dataset(f, engine=""h5netcdf"")
```

#### Expected Output

No output at all.

#### Problem Description

Results in `AttributeError`:

```
Traceback (most recent call last):
  File ""mwe4.py"", line 3, in <module>
    with xarray.open_dataset(f, engine=""h5netcdf"") as ds:
  File ""/media/nas/x21324/miniconda3/envs/py37e/lib/python3.7/site-packages/xarray/backends/api.py"", line 535, in open_dataset
    ds = maybe_decode_store(store)
  File ""/media/nas/x21324/miniconda3/envs/py37e/lib/python3.7/site-packages/xarray/backends/api.py"", line 450, in maybe_decode_store
    use_cftime=use_cftime,
  File ""/media/nas/x21324/miniconda3/envs/py37e/lib/python3.7/site-packages/xarray/conventions.py"", line 570, in decode_cf
    vars, attrs = obj.load()
  File ""/media/nas/x21324/miniconda3/envs/py37e/lib/python3.7/site-packages/xarray/backends/common.py"", line 123, in load
    (_decode_variable_name(k), v) for k, v in self.get_variables().items()
  File ""/media/nas/x21324/miniconda3/envs/py37e/lib/python3.7/site-packages/xarray/backends/h5netcdf_.py"", line 156, in get_variables
    (k, self.open_store_variable(k, v)) for k, v in self.ds.variables.items()
  File ""/media/nas/x21324/miniconda3/envs/py37e/lib/python3.7/site-packages/xarray/core/utils.py"", line 402, in FrozenDict
    return Frozen(dict(*args, **kwargs))
  File ""/media/nas/x21324/miniconda3/envs/py37e/lib/python3.7/site-packages/xarray/backends/h5netcdf_.py"", line 156, in <genexpr>
    (k, self.open_store_variable(k, v)) for k, v in self.ds.variables.items()
  File ""/media/nas/x21324/miniconda3/envs/py37e/lib/python3.7/site-packages/xarray/backends/h5netcdf_.py"", line 120, in open_store_variable
    dimensions = var.dimensions
  File ""/media/nas/x21324/miniconda3/envs/py37e/lib/python3.7/site-packages/h5netcdf/core.py"", line 114, in dimensions
    self._dimensions = self._lookup_dimensions()
  File ""/media/nas/x21324/miniconda3/envs/py37e/lib/python3.7/site-packages/h5netcdf/core.py"", line 98, in _lookup_dimensions
    for axis, dim in enumerate(self._h5ds.dims):
AttributeError: 'Datatype' object has no attribute 'dims'
```

#### Output of ``xr.show_versions()``
<details>
INSTALLED VERSIONS
------------------
commit: None
python: 3.7.3 | packaged by conda-forge | (default, Jul  1 2019, 21:52:21)
[GCC 7.3.0]
python-bits: 64
OS: Linux
OS-release: 4.12.14-lp150.12.79-default
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_GB.UTF-8
LOCALE: en_GB.UTF-8
libhdf5: 1.10.5
libnetcdf: 4.7.1

xarray: 0.14.1
pandas: 0.25.3
numpy: 1.17.3
scipy: 1.3.2
netCDF4: 1.5.3
pydap: None
h5netcdf: 0.7.4
h5py: 2.10.0
Nio: None
zarr: 2.3.2
cftime: 1.0.4.2
nc_time_axis: None
PseudoNetCDF: None
rasterio: 1.1.0
cfgrib: None
iris: None
bottleneck: None
dask: 2.8.0
distributed: 2.8.0
matplotlib: 3.1.2
cartopy: 0.17.0
seaborn: None
numbagg: None
setuptools: 41.6.0.post20191101
pip: 19.3.1
conda: None
pytest: 5.3.0
IPython: 7.9.0
sphinx: 2.2.1
</details>
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