Convergence: Fix to use cache_data for nested stack
Convergence: Fix to use cache_data for nested stack

Fix FnGetRefId of StackResource(nested stack) to fetch value from
cache_data, if present.

(Refer Icd92f6514c7590c90da2fcd2123d33862d613486)
Closes-Bug: #1495546

Change-Id: I3282ae1a07389f54b08c54bf8e7090bbee4c8a50

noironetworks/heat,pratikmallya/heat,dragorosson/heat,gonzolino/heat,cwolferh/heat-scratch,dragorosson/heat,jasondunsmore/heat,openstack/heat,openstack/heat,pratikmallya/heat,jasondunsmore/heat,cwolferh/heat-scratch,dims/heat,steveb/heat,gonzolino/heat,maestro-hybrid-cloud/heat,noironetworks/heat,dims/heat,steveb/heat,maestro-hybrid-cloud/heat