run.log_table stores 1-item lists differently

The following code:
```
run.log_table('test',value={'x':['asd','sdf'],'y':[1,2]})
run.log_table('test1',value={'x':['asd'],'y':[1]})
run.get_metrics()
```
will yield:
`{'test': {'x': ['asd', 'sdf'], 'y': [1, 2]}, 'test1': {'x': 'asd', 'y': 1}}`

It shows that single-item lists are stored differently than lists with multiple items.

This makes the JSON produced from these inconsistent types hard to parse down the line (e.g. outside of AML as in PowerBI for example).

If we pass in a list, we would expect that it is stored as a list even if there is only one item in the list.

---
#### Document Details

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* ID: 2e24ac95-7027-6a3c-81e6-f20cc4415219
* Version Independent ID: 9498cdc2-0d04-39a3-08ce-ef9ea8f2d153
* Content: [azureml.core.run.Run class - Azure Machine Learning Python](https://docs.microsoft.com/en-us/python/api/azureml-core/azureml.core.run.run?view=azure-ml-py)
* Content Source: [AzureML-Docset/stable/docs-ref-autogen/azureml-core/azureml.core.run.Run.yml](https://github.com/MicrosoftDocs/MachineLearning-Python-pr/blob/live/AzureML-Docset/stable/docs-ref-autogen/azureml-core/azureml.core.run.Run.yml)
* Service: **machine-learning**
* Sub-service: **core**
* GitHub Login: @debfro
* Microsoft Alias: **debfro**