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 
If I run that locally, it will remove all my non-test-related indices. Please, let's not do that! :)

Plus, I really dislike that strategy of cleaning before running tests, instead of doing it after running them. It's easier, but I feel like it's just us being lazy about our clean up process. Though I know some people in the team disagree with this... :)