SaveCredentialsFile() does not store anything

Calling the `SaveCredentialsFile()` method with a filename does nothing

I followed to calls inside until oauth2client.client.Storage.locked_put at which point I see:

```
def locked_put(self, credentials):
"""Write a credential.

The Storage lock must be held when this is called.

Args:
credentials: Credentials, the credentials to store.
"""
raise NotImplementedError
```

I also see that oauth2client is deprecated for a while now. Is this a functionality that was removed or am I doing something wrong?

Start with SaveCredentialsFile() and trace the call into oauth2client.client.Storage.locked_put, as described in the report. Reproduce the call with a filename and determine whether the credentials should be persisted; done means the expected storage behavior is established or the reported failure is fixed and covered by an appropriate test.

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