prevent instance group delete if running jobs

* related to https://github.com/ansible/ansible-tower/issues/7936

awx/main/utils/polymorphic.py

@@ -0,0 +1,12 @@
+
+from django.contrib.contenttypes.models import ContentType
+
+
+def build_polymorphic_ctypes_map(cls):
+    # {'1': 'unified_job', '2': 'Job', '3': 'project_update', ...}
+    mapping = {}
+    for ct in ContentType.objects.filter(app_label='main'):
+        ct_model_class = ct.model_class()
+        if ct_model_class and issubclass(ct_model_class, cls):
+            mapping[ct.id] = ct_model_class._camel_to_underscore(ct_model_class.__name__)
+    return mapping