get ssh key in s3 bucket with specific name, load it in StringIO file
        :return:

def get_s3_key(self):
        """
        get ssh key in s3 bucket with specific name, load it in StringIO file
        :return:
        """
        try:
            c = s3.connect_to_region(self._region,
                                     aws_access_key_id=self._aws_access_key_id,
                                     aws_secret_access_key=self._aws_secret_access_key)
            bucket = c.get_bucket(self._s3_bucket)
            key = bucket.get_key(self._s3_name)
            self._key_file = StringIO(unicode(key.get_contents_as_string().decode()))
            self._key_file.seek(0)
            key.close()
        except NoAuthHandlerFound:
            raise SergentSshException('Boto said that you should check your credentials')
        except S3ResponseError as e:
            logger.exception(e)
            raise SergentSshException('bucket %s or key %s not found' % (self._s3_bucket, self._s3_name))