Move recipes to their own subdirectory

This will help remove confusion when depot_tools' recipes.py
ends up in PATH.

BUG=699120

Change-Id: Id4c21b0cc6bb022ea2c21145abe76bebb0a8d9c1
Reviewed-on: https://chromium-review.googlesource.com/458430
Commit-Queue: Paweł Hajdan Jr. <phajdan.jr@chromium.org>
Reviewed-by: Robbie Iannucci <iannucci@chromium.org>

.gitignore

@@ -63,6 +63,7 @@
 # Ignore recipe working directory.
 /.recipe_deps
 /infra/.recipe_deps
+/recipes/.recipe_deps
 
 # Ignore google AE downloaded for running testing only.
 testing_support/google_appengine

infra/config/recipes.cfg

 {
   "api_version": 1,
   "project_id": "depot_tools",
+  "recipes_path": "recipes",
   "deps": [
     {
       "project_id": "recipe_engine",