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 (e.g., from the command line).

Test Plan: Ran a build through Drydock/Harbormaster locally.

Reviewers: chad, tycho.tatitscheff

Reviewed By: chad, tycho.tatitscheff

Subscribers: tycho.tatitscheff

Maniphest Tasks: T9669

Differential Revision: https://secure.phabricator.com/D14368