exception_tracker: use a default value of exception store that is working across all instances e.g vcsserver and enterprise.

rhodecode/config/middleware.py

@@ -436,8 +436,8 b' def _sanitize_vcs_settings(settings):'
 
 
 def _sanitize_cache_settings(settings):
-
-    default_cache_dir = os.path.join(tempfile.gettempdir(), 'rc_cache')
+    temp_store = tempfile.gettempdir()
+    default_cache_dir = os.path.join(temp_store, 'rc_cache')
 
     # save default, cache dir, and use it for all backends later.
     default_cache_dir = _string_setting(
@@ -453,7 +453,7 b' def _sanitize_cache_settings(settings):'
     _string_setting(
         settings,
         'exception_tracker.store_path',
-        default_cache_dir, lower=False)
+        temp_store, lower=False, default_when_empty=True)
 
     # cache_perms
     _string_setting(