MaxWhileTries: Optionally store an exception

So that we can react based on an exception raised while retrying whatever action
ended up not succeeding.

Signed-off-by: Zack Cerza <zack@cerza.org>

Author: zmc

teuthology/contextutil.py

@@ -3,6 +3,8 @@
 import logging
 import time
 
+from typing import Optional
+
 from teuthology.config import config
 from teuthology.exceptions import MaxWhileTries
 
@@ -120,7 +122,7 @@ def _make_error_msg(self):
         )
         return msg
 
-    def __call__(self):
+    def __call__(self, last_exception: Optional[Exception] = None):
         self.counter += 1
         if self.counter == 1:
             return True
@@ -131,7 +133,7 @@ def must_stop():
             (self.timeout == 0 and must_stop())):
             error_msg = self._make_error_msg()
             if self._raise:
-                raise MaxWhileTries(error_msg)
+                raise MaxWhileTries(error_msg, last_exception)
             else:
                 log.warning(error_msg)
                 return False

teuthology/exceptions.py

@@ -1,3 +1,5 @@
+from typing import Optional
+
 class BranchNotFoundError(ValueError):
     def __init__(self, branch, repo=None):
         self.branch = branch
@@ -200,7 +202,14 @@ class SkipJob(Exception):
 
 
 class MaxWhileTries(Exception):
-    pass
+    def __init__(self, message: str = '', last_exception: Optional[Exception] = None):
+        self.message = message
+        self.last_exception = last_exception
+
+    def __str__(self):
+        if self.last_exception:
+            return f"{self.message} (last exception: {self.last_exception})"
+        return self.message
 
 
 class ConsoleError(Exception):