install-devstack-xen.sh: disable secure delete
install-devstack-xen.sh: amend comment, and move tempest block (safe)
install-devstack-xen.sh: remove domU memory setting, move compute block
install-devstack-xen.sh - move image block (safe)
install-devstack-xen.sh: move around OSDOMU_VDI_GB, and amend comments