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/tasks.py

@@ -50,7 +50,7 @@ from awx import celery_app
 from awx.main.constants import CLOUD_PROVIDERS, PRIVILEGE_ESCALATION_METHODS
 from awx.main.models import * # noqa
 from awx.main.models.unified_jobs import ACTIVE_STATES
-from awx.main.exceptions import AwxTaskError, TaskCancel, TaskError
+from awx.main.exceptions import AwxTaskError
 from awx.main.queue import CallbackQueueDispatcher
 from awx.main.expect import run, isolated_manager
 from awx.main.utils import (get_ansible_version, get_ssh_version, decrypt_field, update_scm_url,
@@ -81,7 +81,7 @@ logger = logging.getLogger('awx.main.tasks')
 
 class LogErrorsTask(Task):
     def on_failure(self, exc, task_id, args, kwargs, einfo):
-        if isinstance(exc, AwxTaskError):
+        if getattr(exc, 'is_awx_task_error', False):
             # Error caused by user / tracked in job output
             logger.warning(str(exc))
         elif isinstance(self, BaseTask):
@@ -913,9 +913,9 @@ class BaseTask(LogErrorsTask):
             # Raising an exception will mark the job as 'failed' in celery
             # and will stop a task chain from continuing to execute
             if status == 'canceled':
-                raise TaskCancel(instance, rc)
+                raise AwxTaskError.TaskCancel(instance, rc)
             else:
-                raise TaskError(instance, rc)
+                raise AwxTaskError.TaskError(instance, rc)
 
     def get_ssh_key_path(self, instance, **kwargs):
         '''