Namespace SHA256SUMS file to distro/release/arch
Namespace SHA256SUMS file to distro/release/arch

Its possible other images will want to use the same filename

Change-Id: Iae393bfc71205d39e2bc6e12f5524824607d6101

rdo-management/diskimage-builder,qwefi/tripleo-image-elements,openstack/tripleo-image-elements,CSC-IT-Center-for-Science/diskimage-builder,agroup/tripleo-puppet-elements,citrix-openstack-build/diskimage-builder,agroup/tripleo-puppet-elements,zioproto/diskimage-builder,qwefi/tripleo-image-elements,citrix-openstack-build/diskimage-builder,NaohiroTamura/diskimage-builder,agroup/tripleo-puppet-elements,eantyshev/diskimage-builder,qwefi/tripleo-image-elements,openstack/diskimage-builder,JioCloud/diskimage-builder,zioproto/diskimage-builder,agroup/tripleo-puppet-elements,openstack/diskimage-builder,eantyshev/diskimage-builder,switch-ch/diskimage-builder,radez/tripleo-image-elements,qwefi/tripleo-image-elements,rdo-management/diskimage-builder,rdo-management/tripleo-image-elements,JioCloud/diskimage-builder,varunarya10/diskimage-builder,takahashinobuyuki/diskimage-builder,NaohiroTamura/diskimage-builder,rdo-management/tripleo-image-elements,qwefi/tripleo-image-elements,takahashinobuyuki/diskimage-builder,radez/tripleo-image-elements,CSC-IT-Center-for-Science/diskimage-builder,openstack/tripleo-image-elements,switch-ch/diskimage-builder,varunarya10/diskimage-builder