Compromised VM can make arbitrary blobstore deletes

AgentClient#handle_method (lines 264-303) processes every NATS reply. It calls inject_compile_log (line 273) on every response, which reads response['value']['result']['compile_log_id'] (line 332-338) and passes it to download_and_delete_blob. Separately, any response containing 'exception' goes through format_exception (lines 308-325), which reads exception['blobstore_id'] and also calls download_and_delete_blob. That helper (lines 344-349) calls ResourceManager#get_resource(blob_id) and, in an ensure block, ResourceManager#delete_resource(blob_id). ResourceManager (resource_manager.rb:62-70) calls blobstore.delete(id) on the single shared Director blobstore with no UUID-format check, no ownership check, and no namespace prefix. Affected versions: BOSH Director: All versions prior to v282.1.12