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

scripts/slave/recipes/skia/swarm_trigger.expected/Test-Ubuntu-Clang-GCE-CPU-AVX2-x86_64-Coverage-Trybot.json

 [
   {
     "cmd": [
       "git",
       "remote",
       "set-url",
       "origin",
       "https://skia.googlesource.com/skia.git"
     ],
     "cwd": "[SLAVE_BUILD]/skia",
@@ skipping 445 matching lines @@
       "@@@STEP_LOG_LINE@json.output@  \"upload_dm_results\": false, @@@",
       "@@@STEP_LOG_LINE@json.output@  \"upload_perf_results\": false@@@",
       "@@@STEP_LOG_LINE@json.output@}@@@",
       "@@@STEP_LOG_END@json.output@@@"
     ]
   },
   {
     "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",
       "[SLAVE_BUILD]/skia/infra/bots/assets/skp/VERSION",
       "/path/to/tmp/"
     ],
     "name": "read skp VERSION"
   },
   {
     "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",
       "[SLAVE_BUILD]/skia/infra/bots/assets/skimage/VERSION",
       "/path/to/tmp/"
     ],
     "name": "read skimage VERSION"
   },
   {
     "cmd": [
       "python",
       "-u",
       "\nimport sys, os\npath = sys.argv[1]\nmode = int(sys.argv[2])\nif not os.path.isdir(path):\n  if os.path.exists(path):\n    print \"%s exists but is not a dir\" % path\n    sys.exit(1)\n  os.makedirs(path, mode)\n",
@@ skipping 288 matching lines @@
     },
     "name": "gsutil upload raw coverage data",
     "~followup_annotations": [
       "@@@STEP_LINK@gsutil.upload@https://storage.cloud.google.com/skia-infra/coverage-raw-v1/trybot/2012/05/14/12/Test-Ubuntu-Clang-GCE-CPU-AVX2-x86_64-Coverage-Trybot/5/500/9046e2e693bb92a76e972b694580e5d17ad10748.cov@@@"
     ]
   },
   {
     "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",
       "[SLAVE_BUILD]/swarming_temp_dir/outputs/test_skia/0/nanobench_9046e2e693bb92a76e972b694580e5d17ad10748.json",
       "[SLAVE_BUILD]/swarming_temp_dir/outputs/test_skia/0/nanobench_9046e2e693bb92a76e972b694580e5d17ad10748_1408633190.json"
     ],
     "name": "nanobench JSON"
   },
   {
     "cmd": [
       "python",
       "-u",
       "\nimport os\nimport sys\nos.remove(sys.argv[1])\n",
@@ skipping 24 matching lines @@
     "env": {
       "AWS_CREDENTIAL_FILE": "[HOME]/chromium-skia-gm.boto",
       "BOTO_CONFIG": "[HOME]/chromium-skia-gm.boto"
     },
     "name": "upload nanobench coverage results"
   },
   {
     "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",
       "[SLAVE_BUILD]/swarming_temp_dir/outputs/test_skia/0/coverage_by_line_9046e2e693bb92a76e972b694580e5d17ad10748.json",
       "[SLAVE_BUILD]/swarming_temp_dir/outputs/test_skia/0/coverage_by_line_9046e2e693bb92a76e972b694580e5d17ad10748_1408633190.json"
     ],
     "name": "Line-by-line coverage JSON"
   },
   {
     "cmd": [
       "python",
       "-u",
       "\nimport os\nimport sys\nos.remove(sys.argv[1])\n",
@@ skipping 28 matching lines @@
     "~followup_annotations": [
       "@@@STEP_LINK@gsutil.upload@https://storage.cloud.google.com/skia-infra/coverage-json-v1/trybot/2012/05/14/12/Test-Ubuntu-Clang-GCE-CPU-AVX2-x86_64-Coverage-Trybot/5/500/coverage_by_line_9046e2e693bb92a76e972b694580e5d17ad10748_1408633190.json@@@"
     ]
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]