'Unpack tar.gz bundle'

def _unpack_openssl(self):

    if os.path.isdir(self.build_dir):
        shutil.rmtree(self.build_dir)
    os.makedirs(self.build_dir)
    tf = tarfile.open(self.src_file)
    base = 'openssl-{}/'.format(self.version)
    members = tf.getmembers()
    for member in members:
        if (not member.name.startswith(base)):
            raise ValueError(member.name)
        member.name = member.name[len(base):]
    log.info('Unpacking    files    to    {}'.format(self.build_dir))
    tf.extractall(self.build_dir, members)
