recipe engine: extract infra-specific paths out of the engine

recipe_modules/path/api.py

Index: recipe_modules/path/api.py
diff --git a/recipe_modules/path/api.py b/recipe_modules/path/api.py
index fb45a7d80b764256b62569edd56914fc4e6eea05..f26dcb766cec8ba2c7c44f713acd41bd30b8237b 100644
--- a/recipe_modules/path/api.py
+++ b/recipe_modules/path/api.py
@@ -149,7 +149,6 @@ class PathApi(recipe_api.RecipeApi):
 
   def get_config_defaults(self):
     return {
-      'PLATFORM': self.m.platform.name,
       'CURRENT_WORKING_DIR': self._startup_cwd,
       'TEMP_DIR': self._temp_dir,
     }
@@ -180,12 +179,7 @@ class PathApi(recipe_api.RecipeApi):
     if self._config_set:
       return
     self._config_set = True
-
-    path_config = self.m.properties.get('path_config')
-    if path_config in ('kitchen', 'swarming'):
-      self.set_config(path_config)
-    else:
-      self.set_config('buildbot')
+    self.set_config('BASE')
 
   def mock_add_paths(self, path):
     """For testing purposes, assert that |path| exists."""