Add a bit more debugging to the client registry
Add a bit more debugging to the client registry

The service client registry raises an exception in case of
duplicate registration, but it logs absolutely nothing in case
of successful one, which makes life difficult when debugging
issues with plugin registrations.

Add a debug line for the success case as well, which includes
the plugin name and the configuration data that was loaded.

Change-Id: Ic2036e9e2db4b1604a397baa0cfdaee665a477f8

cisco-openstack/tempest,Juniper/tempest,cisco-openstack/tempest,openstack/tempest,masayukig/tempest,openstack/tempest,Juniper/tempest,vedujoshi/tempest,masayukig/tempest,vedujoshi/tempest