'Assuming the cwd is the extracted python package, execute a simple
python setup.py bdist_egg.
:param setup_py - The name of the setup.py file to execute.
:return: The relative path to the resulting egg file or \'\' on failure.'

def _build_egg_using_setup_py(self, setup_py='setup.py'):

    if (not os.path.exists(setup_py)):
        raise Error(('%s    does    not    exist    in    %s' % (setup_py, os.getcwd())))
    egg_subdir = 'dist'
    if os.path.isdir(egg_subdir):
        shutil.rmtree(egg_subdir)
    status = system(("'%s'    %s    bdist_egg" % (sys.executable, setup_py)))
    if status:
        logging.error('bdist_egg    of    setuptools    failed.')
        return ''
    for filename in os.listdir(egg_subdir):
        if filename.endswith('.egg'):
            return os.path.join(egg_subdir, filename)
