Support for custom API_ROOT

Pulp squeezer currently does not support custom API_ROOT environments from Pulp. As an example, the following hotfix can be used if you use / as API_ROOT:

```bash
find . -name pulp.py -exec sed -i '/doc_path/s/\/pulp//g' {} \;
```

Cause: https://github.com/pulp/squeezer/blob/develop/plugins/module_utils/pulp.py#L74
