fix a bug for multi object deletion

This fix a bug for deleting multiple objects.
This change enables swift3 to receive request body
correctly in order to prevent that swift3 does not
return response for multi object deletion request.

Signed-off-by: Kota Tsuyuzaki <tsuyuzaki.kota@lab.ntt.co.jp>
Update README about keystone usage

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>