<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def setup(self):
 """Load backends and plugins. :returns: A `BuildConfiguration` object constructed during backend/plugin loading. """

    return self._load_plugins(
      self._working_set,
      self._bootstrap_options.pythonpath,
      self._bootstrap_options.plugins,
      self._bootstrap_options.backend_packages
    )