Move dscv and ca_certs to config section service_clients

In https://review.openstack.org/#/c/294425/ a new config
section "service_clients" is added which hosts parameters
common to all service clients. ca_certificates_file and
disable_ssl_certificate_validation are also common to all
service clients, so this is to move them from section identity
to section service_clients

Change-Id: I296f1080ce89f0cdceae1c476866b215393b2605
6 files changed