Fix file.copy recipe_module to not fail if files are already equal.

scripts/slave/recipe_modules/chromedriver/example.expected/Android_ChromeDriver_test_failure.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_MODULE[depot_tools::bot_update]/resources/bot_update.py",
       "--spec",
       "cache_dir = '[GIT_CACHE]'\nsolutions = [{'deps_file': '.DEPS.git', 'managed': True, 'name': 'src', 'url': 'https://chromium.googlesource.com/chromium/src.git'}]",
       "--patch_root",
       "src",
@@ skipping 635 matching lines @@
     ],
     "name": "Download Test Results Log.gsutil download results log",
     "~followup_annotations": [
       "@@@STEP_NEST_LEVEL@1@@@"
     ]
   },
   {
     "cmd": [
       "python",
       "-u",
-      "\nimport shutil\nimport sys\nshutil.copy(sys.argv[1], sys.argv[2])\n",
+      "\nimport shutil\nimport sys\n# Apparently, shutil.copy fails if files are binary-equal on *nix OSes.\n# See http://crbug.com/636168#c8.\nif hasattr(shutil, '_samefile'):\n  if shutil._samefile(sys.argv[1], sys.argv[2]):\n    sys.exit(0)\nshutil.copy(sys.argv[1], sys.argv[2])\n",
       "[TMP_BASE]/results_log_tmp_10/android_log.json",
       "/path/to/tmp/"
     ],
     "name": "Download Test Results Log.read results log file",
     "~followup_annotations": [
       "@@@STEP_NEST_LEVEL@1@@@"
     ]
   },
   {
     "cmd": [
@@ skipping 53 matching lines @@
     "~followup_annotations": [
       "@@@STEP_NEST_LEVEL@1@@@"
     ]
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]