Move plugin client registration to proxy

The plugin client registration is triggered to early, which leads
to the CONF object being initialised twice. Moving the plugin
client registration to live together with the tempest own client
registration.

Change-Id: I7c15e8c5ee9c7421ac410cfaa84b3ce21380f5e7

tempest/config.py

@@ -1188,6 +1188,12 @@ class TempestConfigProxy(object):
             # loaded, options registered, and _config is set.
             _register_tempest_service_clients()
 
+            # Registering service clients and pushing their configuration to
+            # the service clients register. Doing this in the config module
+            # ensures that the configuration is available by the time we
+            # discover tests from plugins.
+            plugins.TempestTestPluginManager()._register_service_clients()
+
         return getattr(self._config, attr)
 
     def set_config_path(self, path):

tempest/test_discover/plugins.py

@@ -124,7 +124,6 @@ class TempestTestPluginManager(object):
             'tempest.test_plugins', invoke_on_load=True,
             propagate_map_exceptions=True,
             on_load_failure_callback=self.failure_hook)
-        self._register_service_clients()
 
     @staticmethod
     def failure_hook(_, ep, err):