conf: make 'default' upper case
conf: make 'default' upper case

When api opts were moved from ``DEFAULT`` gorup to ``api`` group
the deprecation group was set to ``default`` instead of ``DEFAULT``.

Implements: bp centralize-config-options-ocata
Change-Id: Iebe97cdf8e06ae7d617dfa3b41ec96cca04db14b

klmitch/nova,phenoxim/nova,rahulunair/nova,Juniper/nova,mahak/nova,jianghuaw/nova,jianghuaw/nova,jianghuaw/nova,gooddata/openstack-nova,openstack/nova,rahulunair/nova,openstack/nova,rajalokan/nova,Juniper/nova,Juniper/nova,vmturbo/nova,klmitch/nova,mahak/nova,vmturbo/nova,vmturbo/nova,klmitch/nova,rahulunair/nova,mahak/nova,mikalstill/nova,openstack/nova,gooddata/openstack-nova,rajalokan/nova,rajalokan/nova,klmitch/nova,vmturbo/nova,hanlind/nova,gooddata/openstack-nova,Juniper/nova,phenoxim/nova,hanlind/nova,jianghuaw/nova,hanlind/nova,mikalstill/nova,rajalokan/nova,gooddata/openstack-nova,mikalstill/nova