use the recommended yaml.safe_load function

reason: with pyyaml >= 5, the load function without Loader is deprecated.
Even if we do not use version 5 for now, we should use good practices.
https://pyyaml.org/wiki/PyYAMLDocumentation#loading-yaml
yaml/pyyaml#257

integration_tests/suite/test_csv_backend.py

@@ -28,7 +28,7 @@ class _BaseCSVFileTestCase(unittest.TestCase):
     def setUp(self):
         config_file = absolute_file_name(self.asset, self.source_config)
         with open(config_file) as f:
-            config = {'config': yaml.load(f)}
+            config = {'config': yaml.safe_load(f)}
         config['config']['file'] = absolute_file_name(self.asset, config['config']['file'][1:])
         self.backend = BackendWrapper('csv', config)
         super().setUp()

wazo_dird/plugins/api/http.py

@@ -23,7 +23,7 @@ def get(self):
         for module in iter_entry_points(group=self.api_entry_point):
             try:
                 plugin_package = module.module_name.rsplit('.', 1)[0]
-                spec = yaml.load(resource_string(plugin_package, self.api_filename))
+                spec = yaml.safe_load(resource_string(plugin_package, self.api_filename))
                 if not spec:
                     logger.debug('plugin has no API spec: %s', plugin_package)
                 else:

wazo_dird/plugins/service_discovery_service/plugin.py

@@ -204,4 +204,4 @@ def generate_from_new_service(self, service, uuid, host, port):
         template_args['port'] = port
 
         yaml_representation = template.render(template_args)
-        return yaml.load(yaml_representation)
+        return yaml.safe_load(yaml_representation)