The devstack default limit enforcement for glance defaults
to 1GB, and unfortunately this is too small for many to use
larger images such as centos which includes hardware firmware
images for execution on baremetal where drivers need the vendor
blobs in order to load/run.
Sets ironic-base to 5GB, and updates examples accordingly.
Depends-On: https://review.opendev.org/c/openstack/devstack/+/801309
Change-Id: I41294eb571d07a270a69e5b816cdbad530749a94
b5872c9032