R1:f48a8337048d

Fix an issue with incorrect authorization handling in Working Copy build steps

Summary:
Fixes T9669. Two issues:

- We were using `repositoryPHIDs` instead of `blueprintPHIDs` for the list of allowed blueprints. Use the correct value.
- We weren't enforcing `allowedBlueprintPHIDs` fully correctly. We //did// require an authorization, so the net effect was correct in nearly all cases, but we could have selected from too large a pool in the case where the application itself was doing the authorization…