Use config fixture from oslo.config
Use config fixture from oslo.config

With the release of oslo.config 1.4.0.0a1, oslo.config
contains the config fixture. Keystone was using the config
fixture in oslo-incubator's fixture module. With this change
Keystone is using the config fixture in oslo.config

Change-Id: Id03efdfbe8893c48a9ad65f0cf59e1dbae03dc47

rajalokan/keystone,openstack/keystone,takeshineshiro/keystone,vivekdhayaal/keystone,roopali8/keystone,rushiagr/keystone,mahak/keystone,jonnary/keystone,ging/keystone,takeshineshiro/keystone,vivekdhayaal/keystone,roopali8/keystone,nuxeh/keystone,himanshu-setia/keystone,ging/keystone,himanshu-setia/keystone,jumpstarter-io/keystone,maestro-hybrid-cloud/keystone,dstanek/keystone,openstack/keystone,jamielennox/keystone,MaheshIBM/keystone,idjaw/keystone,vivekdhayaal/keystone,jamielennox/keystone,blueboxgroup/keystone,rajalokan/keystone,jumpstarter-io/keystone,klmitch/keystone,UTSA-ICS/keystone-kerberos,nuxeh/keystone,ajayaa/keystone,openstack/keystone,klmitch/keystone,rodrigods/keystone,idjaw/keystone,rushiagr/keystone,dstanek/keystone,promptworks/keystone,nuxeh/keystone,dims/keystone,ilay09/keystone,mahak/keystone,cernops/keystone,ajayaa/keystone,dstanek/keystone,rushiagr/keystone,promptworks/keystone,ilay09/keystone,mahak/keystone,rajalokan/keystone,MaheshIBM/keystone,cernops/keystone,maestro-hybrid-cloud/keystone,blueboxgroup/keystone,UTSA-ICS/keystone-kerberos,promptworks/keystone,jumpstarter-io/keystone,jonnary/keystone,ilay09/keystone,dims/keystone,rodrigods/keystone