Adding support for --worker-config in 'iron_worker run'

Adds ability to supply config both with --config (option already present but not used) and --worker-config CONFIG_FILE, same as when uploading. If both switches are present, --worker-config takes precedence

```
$ iron_worker run local_run_with_config.worker --worker-config local_run_with_config.json
$ iron_worker run local_run_with_config.worker --config '{"foo":"bar"}'
```
Please forgive me if I'm not following your standards, it's a massive codebase and this fix was made a bit quick-and-dirty.

Thanks
/Lars