Updated openstack/openstack
Project: openstack/taskflow  188ccbd09e396665567720861f5578887814de70

Be smarter about required flow symbols

Instead of blindly assuming all the symbols that
are provided automatically work for all flows even
if the flow has ordering constraints we should set
the base flow class requires property to be abstract
and provide flow specific properties that can do the
appropriate analysis to determine what the flows
unsatisfied symbol requirements actually are.

Part of blueprint taskflow-improved-scoping

Change-Id: Ie149c05b3305c5bfff9d9f2c05e7e064c3a6d0c7