When the dep_attrs function was written, it was used only in convergence
after checking a single resource. However, now we also use it to generate
data for the ResourceProxy objects, which is often done for all resources
simultaneously. That means doing O(n^2) dep_attrs() calls, which can really
slow things down when there is a large number of resources with complex
properties (or metadata).
This change adds an all_dep_attrs() call, which runs as fast as dep_attrs()
on everything except get_attr functions and their arguments, but only needs
to be called once instead of once per resource. (The get_attr function can
in future override the default implementation of all_dep_attrs() to be as
efficient as dep_attrs() as well.) The resulting data is cached in the
ResourceDefinition or OutputDefinition so that subsequent calls to their
get_attr() methods with different (or the same) resource names will use the
existing data.
Change-Id: If95f4c04b841519ce3d7492211f2696588c0ed48
Partially-Implements: blueprint stack-definition
Closes-Bug: #1684272
3c13cb82a6