[BZ 1136998] Fix the logic in the upgrade delegate.

It now better distinguishes between configuration values coming from a
previous upgrade report in the chain versus the values coming from
the existing resource.

Being aware of the distinction is needed for a correct decision on what
value should the "supportsPatching" attribute set to.

(cherry picked from commit 1759352ee3ca4f184872aa55d9530d54a12c42df)