Propose a task/flow tracking mechanism in cinder for juno

Create a proposal to increase the usefulness of taskflow in cinder
by taking advantage of the taskflow engine event stream/notification
mechansim so that the taskflow engine is not a black box but is a more
understandable and user friendly execution model.

Change-Id: I4cc8d48e969e1f1107cd477ae8e44d8a130dcb7f
Merge "Propose a task/flow tracking mechanism in cinder for juno"