Add BrigadeSubTaskError for grouped tasks

Raises BrigadeSubTaskError when a subtask to a grouped task has failed,
this allows for a prettier error message when using print_output()

brigade/core/exceptions.py

@@ -51,3 +51,24 @@ def __str__(self):
                 text += "**** {}\n".format(sub_r.name)
                 text += "{}\n".format(sub_r)
         return text
+
+class BrigadeSubTaskError(Exception):
+    """
+    Raised by brigade when a sub task managed by :meth:`brigade.core.Task.run`
+    has failed
+
+    Arguments:
+        task (str): Name of the sub task that failed
+    Attributes:
+        task (str): Name of the sub task that failed
+    """
+
+    def __init__(self, task):
+        self.task = task
+
+    def __str__(self):
+        text = "\n"
+        text += "{}\n".format("#" * 40)
+        text += "# Subtask: {} (failed)\n".format(self.task)
+        text += "{}\n".format("#" * 40)
+        return text

brigade/core/task.py

@@ -3,6 +3,7 @@
 from builtins import super
 
 from brigade.core.exceptions import BrigadeExecutionError
+from brigade.core.exceptions import BrigadeSubTaskError
 
 
 class Task(object):
@@ -61,10 +62,17 @@ def start(self, host, brigade):
             r = self.task(self, **self.params)
             if not isinstance(r, Result):
                 r = Result(host=host, result=r)
+
+        except BrigadeSubTaskError as e:
+            tb = traceback.format_exc()
+            logger.error("{}: {}".format(self.host, tb))
+            r = Result(host, exception=e, result=str(e), failed=True)
+
         except Exception as e:
             tb = traceback.format_exc()
             logger.error("{}: {}".format(self.host, tb))
             r = Result(host, exception=e, result=tb, failed=True)
+
         r.name = self.name
         r.severity_level = logging.ERROR if r.failed else self.severity_level
 
@@ -93,11 +101,12 @@ def grouped_tasks(task):
         if "severity_level" not in kwargs:
             kwargs["severity_level"] = self.severity_level
         r = Task(task, **kwargs).start(self.host, self.brigade)
+        self.results.append(r[0] if len(r) == 1 else r)
+
         if r.failed:
             # Without this we will keep running the grouped task
-            raise r.exception
+            raise BrigadeSubTaskError((r.name))
 
-        self.results.append(r[0] if len(r) == 1 else r)
         return r
 
     def is_dry_run(self, override=None):