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 
@AdrianGaudebert, history (me) has perpetuated an unfortunate naming convention that makes this issue unclear.  A more appropriate name for the ```ConnectionContext``` class would be ```ConnectionFactory```.  This class is responsible for all of the details of connecting to a resource, including instantiating the "native" connection class, and then returning it "skinned" with a lightweight wrapper: the ```Connection``` class.   The wrapper is optional and controlled by specifying the wrapper class name in configman.  If the act of connecting were to be moved to the connection class, then the wrapping would be mandatory rather than optional.  The PG, RMQ and HappyBase classes are the best examples of this form, whereas the HBase & HB classes blur the distinction.