Fix --key flag/env variable precendece

[JakeDawkins]

Problem

• When running the Apollo CLI from a repo that has an apollo.config.js file, the config's engine service name always took precedence over a passed in --key flag and/or environment variables.

Solution

• Make sure that the config loader uses the proper service/client name.
• If there's a name passed in (from .env file or from flags), it should overwrite the client.service/service.name from the loaded file.