Revert NestedStack FnGetRefId changes

This partially reverts commit e376c83cbd57c0720336848e4b82e3b7b804a347.

Allow StackResource to set the resource_id, since it will be the one
retrieving the stack using it.

Fixes bug #1154202

Change-Id: I2140afb4e9bf89b4eb73e45f4ef5974df98e87e1
Merge "Revert NestedStack FnGetRefId changes"