Fix ```osc build``` interference

When osc.build imported then osc build command fails with:

```
  File "/usr/lib/python2.7/site-packages/osc/commandline.py", line 5676, in do_build
    return osc.build.main(self.get_api_url(), opts, args)
  File "/usr/lib/python2.7/site-packages/osc/build.py", line 523, in main
    build_root = config['api_host_options'][apiurl].get('build-root', build_root)
KeyError: 'api_host_options'
```