Fix bug in dockerloadformat and make sure we handle exceptions properly in the verb call

util/queuefile.py

@@ -12,6 +12,11 @@ class QueueFile(object):
     self._buffer = ''
     self._total_size = 0
     self._name = name
+    self.raised_exception = False
+    self._exception_handlers = []
+
+  def add_exception_handler(self, handler):
+    self._exception_handlers.append(handler)
 
   def read(self, size=8192):
     if self._closed or self._done:
@@ -25,7 +30,11 @@ class QueueFile(object):
 
       if isinstance(result, Exception):
         self._closed = True
-        raise result
+        self.raised_exception = True
+        for handler in self._exception_handlers:
+          handler(result)
+          
+        return
 
       self._buffer += result
       self._total_size += len(result)