Clean up: Get OrganizationSerializer class from viewset utility fn

onadata/apps/api/viewsets/organization_profile_viewset.py

@@ -130,7 +130,7 @@ def members(self, request, *args, **kwargs):
 
         serializer.save()
 
-        data = OrganizationSerializer(
+        data = self.serializer_class(
             organization, context={"request": request}
         ).data
         # pylint: disable=attribute-defined-outside-init

onadata/libs/utils/cache_tools.py

@@ -7,6 +7,8 @@
 from django.core.cache import cache
 from django.utils.encoding import force_bytes
 
+from onadata.libs.permissions import ROLES_ORDERED
+
 # Cache names used in project serializer
 PROJ_PERM_CACHE = "ps-project_permissions-"
 PROJ_NUM_DATASET_CACHE = "ps-num_datasets-"