Updated openstack/openstack
Project: openstack/taskflow  24a5b6ffec3c8063102540526526b20b7aa3356b

Expand documention on failures and wrapped failures types

To make it more clear why these objects and types exist and when
and why they are used and reraised increase the verbosity of the
comments and associated inline documentation on these two classes
to help explain there existence & usefulness.

Change-Id: I742bbcd69c71df80e6de7becc8aee153bf16b34b