Print info about Docker image used for test run.
Print info about Docker image used for test run.

Prints the following message at the beginning of a test run:

```
Running inside image built at 20210118-122927 for commit 1e7a9242e69f8d998ca753b1734300551d8cdd52
```

This will help debug version mismatch issues Alexis reported.

Kaggle/learntools,Kaggle/learntools