Unable to get aggregation_control.groupby_attrs a

### Description

```
Following [intake-esm doc](https://intake-esm.readthedocs.io/en/stable/how-to/understand-keys-and-how-to-change-them.html) to print aggregation columns and get more info on the keys
1) catalog.esmcat.aggregation_control.groupby_attrs and 2) keys_info(), but running into errors. User error not ruled out, please point me in the right direction.

Background being - I want to get the aggregate columns (and vocabulary url!) from the json and see if we can validate and provide additional info to users regarding the catalog correctness and expected structure before it is used in the analysis.

```

### What I Did

```
cat = intake.open_esm_datastore(col)

>>> cat.keys_info()
Traceback (most recent call last):
File "/nbhome/Aparna.Radhakrishnan/conda/envs/intake/lib/python3.7/site-packages/intake_esm/core.py", line 239, in __getitem__
return self._entries[key]
KeyError: 'keys_info'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "/nbhome/Aparna.Radhakrishnan/conda/envs/intake/lib/python3.7/site-packages/intake/catalog/base.py", line 339, in __getattr__
return self[item] # triggers reload_on_change
File "/nbhome/Aparna.Radhakrishnan/conda/envs/intake/lib/python3.7/site-packages/intake_esm/core.py", line 246, in __getitem__
raise KeyError(key)
KeyError: 'keys_info'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "", line 1, in
File "/nbhome/Aparna.Radhakrishnan/conda/envs/intake/lib/python3.7/site-packages/intake/catalog/base.py", line 341, in __getattr__
raise AttributeError(item)
AttributeError: keys_info

```

```
cat.esmcat.aggregation_control.groupby_attrs
AttributeError: esmcat
>>> type(cat)

>>> catalog.esmcat.aggregation_control.groupby_attrs
Traceback (most recent call last):
File "", line 1, in
NameError: name 'catalog' is not defined
>>> cat.esmcat.aggregation_control.groupby_attrs
Traceback (most recent call last):
File "/nbhome/Aparna.Radhakrishnan/conda/envs/intake/lib/python3.7/site-packages/intake_esm/core.py", line 239, in __getitem__
return self._entries[key]
KeyError: 'esmcat'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "/nbhome/Aparna.Radhakrishnan/conda/envs/intake/lib/python3.7/site-packages/intake/catalog/base.py", line 339, in __getattr__
return self[item] # triggers reload_on_change
File "/nbhome/Aparna.Radhakrishnan/conda/envs/intake/lib/python3.7/site-packages/intake_esm/core.py", line 246, in __getitem__
raise KeyError(key)
KeyError: 'esmcat'
```
### Version information: output of `intake_esm.show_versions()`

The files in csv are NetCDF files that are internal to GFDL.
This is a template of what was used

https://github.com/aradhakrishnanGFDL/CatalogBuilder/blob/main/cats/gfdl_test1.json
and https://github.com/aradhakrishnanGFDL/CatalogBuilder/blob/main/cats/gfdl_test1.csv

intake_esm.__version__
'2020.6.11'