do not use a custom task exception

* Celery + json pickling do not handle custom Exceptions (and may never
do so). Mentioning of, if handling custom Exceptions then the code would
be susceptible to same arbitrary code execution that python pickle is
vulnerable to.
* So don't use custom Exceptions.

awx/main/exceptions.py

@@ -1,24 +1,36 @@
-class AwxTaskError(Exception):
-    """Base exception for errors in unified job runs"""
-    def __init__(self, task, message=None):
+# Copyright (c) 2018 Ansible by Red Hat
+# All Rights Reserved.
+
+# Celery does not respect exception type when using a serializer different than pickle;
+# and awx uses the json serializer
+# https://github.com/celery/celery/issues/3586
+
+
+class _AwxTaskError():
+    def build_exception(self, task, message=None):
         if message is None:
             message = "Execution error running {}".format(task.log_format)
-        super(AwxTaskError, self).__init__(message)
-        self.task = task
- 
- 
-class TaskCancel(AwxTaskError):
-    """Canceled flag caused run_pexpect to kill the job run"""
-    def __init__(self, task, rc):
-        super(TaskCancel, self).__init__(
-            task, message="{} was canceled (rc={})".format(task.log_format, rc))
-        self.rc = rc
+        e = Exception(message)
+        e.task = task
+        e.is_awx_task_error = True
+        return e
+
+    def TaskCancel(self, task, rc):
+        """Canceled flag caused run_pexpect to kill the job run"""
+        message="{} was canceled (rc={})".format(task.log_format, rc)
+        e = self.build_exception(task, message)
+        e.rc = rc
+        e.awx_task_error_type = "TaskCancel"
+        return e
+
+    def TaskError(self, task, rc):
+        """Userspace error (non-zero exit code) in run_pexpect subprocess"""
+        message = "{} encountered an error (rc={}), please see task stdout for details.".format(task.log_format, rc)
+        e = self.build_exception(task, message)
+        e.rc = rc
+        e.awx_task_error_type = "TaskError"
+        return e
 
 
-class TaskError(AwxTaskError):
-    """Userspace error (non-zero exit code) in run_pexpect subprocess"""
-    def __init__(self, task, rc):
-        super(TaskError, self).__init__(
-            task, message="%s encountered an error (rc=%s), please see task stdout for details.".format(task.log_format, rc))
-        self.rc = rc
+AwxTaskError = _AwxTaskError()