[engine] make Uncaught Exception steps purple.

recipe_engine/step_runner.py

Index: recipe_engine/step_runner.py
diff --git a/recipe_engine/step_runner.py b/recipe_engine/step_runner.py
index 542ac26dde97c928b37107f99b55bc013e5ae84f..7f81fccb0fcec27446de16dea3fc824a644b6213 100644
--- a/recipe_engine/step_runner.py
+++ b/recipe_engine/step_runner.py
@@ -179,6 +179,7 @@ class SubprocessStepRunner(StepRunner):
       step_config = None  # Make sure we use rendered step config.
     except:
       with self.stream_engine.make_step_stream('Placeholder Exception') as s:
+        s.set_step_status('EXCEPTION')
         with s.new_log_stream('exception') as l:
           l.write_split(traceback.format_exc())
       raise
@@ -424,6 +425,7 @@ class SimulationStepRunner(StepRunner):
       step_config = None  # Make sure we use rendered step config.
     except:
       with self.stream_engine.make_step_stream('Placeholder Exception') as s:
+        s.set_step_status('EXCEPTION')
         with s.new_log_stream('exception') as l:
           l.write_split(traceback.format_exc())
       raise