Add PDB on exception debug tool and config setting

apps/common/debug.py

@@ -0,0 +1,16 @@
+import sys, pdb
+
+previous_except_hook = None
+
+
+def except_hook(exctype, value, traceback):
+    if previous_except_hook:
+        previous_except_hook(exctype, value, traceback)
+
+    pdb.post_mortem(traceback)
+
+
+def insert_pdb_exception_hook():
+    previous_except_hook = sys.excepthook
+    sys.excepthook = except_hook
+