The default_domain_id is used to specify a domain when the client
hasn't explicitly set one. It defaults to 'default' which is fine
for liberty and previous because the id of the default domain is,
oddly, 'default' rather than a uuid. On Mitaka and higher it is
a uuid so when keystone assumes the default domains id is 'default'
it fails.
Change-Id: Iaa5e6a07a229815cf2281858cb68a4e120aa2af3
Closes-Bug: 1626889