bug 1513346: Rely on chaining for rollback errors
bug 1513346: Rely on chaining for rollback errors

In transaction_context, log rollback errors, but also raise them so they
are chained to the original exception.

lonnen/socorro,mozilla/socorro,mozilla/socorro,lonnen/socorro,mozilla/socorro,mozilla/socorro,lonnen/socorro,mozilla/socorro,lonnen/socorro,mozilla/socorro