Add default value for CONF.auth.admin_domain_name

It's a bit confusing for the users who are not so familiar
with keystone v3 to configure the value of CONF.auth.admin_domain_name,
so better to provide a default value for this config item,
which can work in most environments.

Change-Id: I21705f6c4966e507e31201e3efe6d0d593526020
1 file changed