bug 1094767; crashstorage type for new ES module

This PR introduces a crashstorage type for the new ES module.  It also modifies the `ConnectionContext` class to bring it in line with the patterns established in the other `external` modules.  The changes to the context required some other modifications to be made to the index creation class (and associated tests).

`r?` @AdrianGaudebert @twobraids 
Those don't work like you expect them to. In the first case, ``operational_exceptions`` is equal to ``elasticsearch.exceptions.ConnectionError``, because the parenthesis are not considered to be a tuple declaration. You either need to add a comma after the first element, or to explicit the tuple declaration (probably better). 

```python
operational_exceptions = tuple(
    elasticsearch.exceptions.ConnectionError,
)
conditional_exceptions = tuple()
```