conf: refactor conf_fixture.py
conf: refactor conf_fixture.py

Tidied up the conf_fixture.py file. Sorted all defaults by group and conf
name.

Change-Id: Ifa25daa28a2c2a606efa83905e4bf0720dd31fac
Implements: blueprint centralize-config-options-ocata

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