registration: Make it easier for other code to get extension metadata

registration: Make it easier for other code to get extension metadata

Right now if other code wanted to access extension metadata from
extension.json, it would have to either re-implement parts of
loadFromQueue() or make assumptions about the processor and schema being
used.

Lets split that code out in to a public readFromQueue() function that
returns all extracted data from the processors.

Change-Id: I314d73341d3faaa47e01f722123c20fd8f61da8a