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 
We usually use ``ok_`` and ``eq_`` from the ``nose`` module for those things. ``assert`` should be used only in rare cases, when you want to assert something that is not related to the current test.