Remove remaining usage of six
Remove remaining usage of six

This removes the remaining usage of six, which is a leftover of
the previous removal patch[1].

[1] 53abb1b2f6e9d02e549cef20c71d58290433d0e2

Change-Id: Ie94c712d8b2baaff6066ce924573f6f152b921fe

openstack/storlets,openstack/storlets,openstack/storlets,openstack/storlets