Revert "Move taskflow.utils.misc.Failure to its own module"

This reverts commit 42ca240e8157b840c298d14fbf478ae570376633 which
was a breaking change in a library consumed by other OpenStack
projects with no deprecation or backwards compatibility
considerations. It was able to merge because openstack/taskflow is
apparently not yet part of the integrated gate via the proposed
I202f4809afd689155e2cc4a00fc704fd772a0e92 change.

Change-Id: I96cf36dc317499df91e43502efc85221f8177395
Closes-Bug: #1300161