Recipes: make cwd default to slave_build

scripts/slave/recipes/example/defer_multiple.expected/nested_normal_fail.json

Index: scripts/slave/recipes/example/defer_multiple.expected/nested_normal_fail.json
diff --git a/scripts/slave/recipes/example/defer_multiple.expected/nested_normal_fail.json b/scripts/slave/recipes/example/defer_multiple.expected/nested_normal_fail.json
index e517c294dcba0402238e8d0c9deb1da4bc30f733..a06916761b20d6594175c06db669554f5c596b8c 100644
--- a/scripts/slave/recipes/example/defer_multiple.expected/nested_normal_fail.json
+++ b/scripts/slave/recipes/example/defer_multiple.expected/nested_normal_fail.json
@@ -3,24 +3,28 @@
     "cmd": [
       "true"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "prelude"
   },
   {
     "cmd": [
       "true"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "aggregated start"
   },
   {
     "cmd": [
       "true"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "aggregated finish"
   },
   {
     "cmd": [
       "true"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "normal start",
     "~followup_annotations": [
       "step returned non-zero exit code: 1",
@@ -31,24 +35,28 @@
     "cmd": [
       "true"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "normal finish"
   },
   {
     "cmd": [
       "true"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "composite start"
   },
   {
     "cmd": [
       "true"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "composite finish"
   },
   {
     "cmd": [
       "true"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "clean up"
   },
   {