Stop reading local config for domain-specific SQL config driver
Stop reading local config for domain-specific SQL config driver

When an SQL-config-based domain-specific backend was loaded the
local config file (/etc/keystone/keystone.conf) was also read. The
local config file should not be used in this case.

This caused running the tests locally to fail if there were changes
in /etc/keystone/keystone.conf.

Change-Id: Idd095b2df375329f579c164d00dfd50b41b0e96d
Closes-Bug: 1489118

mahak/keystone,openstack/keystone,mahak/keystone,rajalokan/keystone,openstack/keystone,roopali8/keystone,takeshineshiro/keystone,rajalokan/keystone,maestro-hybrid-cloud/keystone,ajayaa/keystone,idjaw/keystone,dims/keystone,openstack/keystone,klmitch/keystone,ilay09/keystone,maestro-hybrid-cloud/keystone,ilay09/keystone,rajalokan/keystone,himanshu-setia/keystone,takeshineshiro/keystone,ilay09/keystone,dims/keystone,ajayaa/keystone,idjaw/keystone,cernops/keystone,himanshu-setia/keystone,mahak/keystone,jonnary/keystone,klmitch/keystone,cernops/keystone,roopali8/keystone,jonnary/keystone