Manual roll of recipe_engine

Needed because bad change broke the recipe engine

BUG=696100
TBR=iannucci

Change-Id: Ia8a293a22ead5654313b5bdcdaaf475f41e96519
Reviewed-on: https://chromium-review.googlesource.com/446869Reviewed-by: Robbie Iannucci <iannucci@chromium.org>
Reviewed-by: Stephen Martinis <martiniss@chromium.org>
Commit-Queue: Stephen Martinis <martiniss@chromium.org>

infra/config/recipes.cfg

@@ -5,5 +5,5 @@ deps {
   project_id: "recipe_engine"
   url: "https://chromium.googlesource.com/external/github.com/luci/recipes-py.git"
   branch: "master"
-  revision: "90e24d410ab511aac5cdf0d20ee216cf488aa379"
+  revision: "3f78fe8c06fe1e8e6adf2309645fab4e2a62f821"
 }