[install] replaced 'D' with 'd'
[install] replaced 'D' with 'd'

in finalize the installation step for keystone replaced the DOMAIN_NAME
from 'Default' to 'default'

Change-Id: If12f8156cc5574d6f0676ae77b31167acf3900b6
Closes-Bug:#1636369

openstack/openstack-manuals,openstack/openstack-manuals,openstack/openstack-manuals,openstack/openstack-manuals