1096539 - Adds auto-reconnect support for celery endpoints if Qpidd stops

https://bugzilla.redhat.com/show_bug.cgi?id=1096539

This PR does three things:
* Adds reconnect support for celery endpoints.
* Adds much better test coverage for Transport.establish_connection().
* Also sneaking in a huge doc update for the missing documentation for the FDShimThread and FDShim removal