[recipe_modules/file] add real file module to engine.

recipe_modules/path/examples/full.expected/win_swarming.json

 [
   {
     "cmd": [
       "/bin/echo",
       "[TMP_BASE]\\foo"
     ],
     "name": "step1"
   },
   {
     "cmd": [
@@ skipping 25 matching lines @@
   },
   {
     "cmd": [
       "touch",
       "[HOME]\\file"
     ],
     "name": "touch my home"
   },
   {
     "cmd": [
+      "rm",
+      "-rf",
+      "[START_DIR]\\copy2"
+    ],
+    "name": "rm copy2 (initial)"
+  },
+  {
+    "cmd": [
+      "mkdir",
+      "-p",
+      "[START_DIR]\\copy1\\foo\\bar"
+    ],
+    "name": "mkdirs"
+  },
+  {
+    "cmd": [
+      "cp",
+      "-a",
+      "[START_DIR]\\copy1",
+      "[START_DIR]\\copy2"
+    ],
+    "name": "cp copy1 copy2"
+  },
+  {
+    "cmd": [
+      "rm",
+      "-rf",
+      "[START_DIR]\\copy2\\foo"
+    ],
+    "name": "rm copy2/foo"
+  },
+  {
+    "cmd": [
+      "rm",
+      "-rf",
+      "[START_DIR]\\copy2"
+    ],
+    "name": "rm copy2"
+  },
+  {
+    "cmd": [
       "echo",
       "[START_DIR]\\some\\thing"
     ],
     "name": "converted path [START_DIR]\\some\\thing"
   },
   {
     "cmd": [
       "echo",
       "[START_DIR]"
     ],
@@ skipping 26 matching lines @@
       "RECIPE[recipe_engine::path:examples/full].resources"
     ],
     "name": "converted path RECIPE[recipe_engine::path:examples/full].resources"
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]