This refactors the building of schema from parameter validation to use a
new method (which doesn't keep stacks in memory), and use that new
method for providing proper schema for resource group when the size is
0.
Change-Id: Id3020e8f3fd94e2cef413d5eb9de9d1cd16ddeaa
Closes-Bug: #1751074
Closes-Bug: #1626025