Recipes: make cwd default to slave_build

scripts/slave/recipes/syzygy/coverage.expected/full_master_client_syzygy_Syzygy_Coverage.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "[BUILD]\\scripts\\slave\\kill_processes.py"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "taskkill"
   },
   {
     "cmd": [
       "python",
       "-u",
       "[DEPOT_TOOLS]\\gclient.py",
       "config",
       "--spec",
       "cache_dir = None\nsolutions = [{'deps_file': 'DEPS.syzygy', 'managed': False, 'name': 'src', 'url': 'https://github.com/google/syzygy.git'}, {'deps_file': 'DEPS', 'managed': False, 'name': 'src-internal', 'url': 'svn://svn.chromium.org/chrome-internal/trunk/syzygy/internal.DEPS'}]"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "gclient setup"
   },
   {
     "cmd": [
       "python",
       "-u",
       "[DEPOT_TOOLS]\\gclient.py",
       "sync",
       "--nohooks",
       "--force",
       "--verbose",
       "--delete_unversioned_trees",
       "--revision",
       "src@0e9f25b1098271be2b096fd1c095d6d907cf86f7",
       "--output-json",
       "/path/to/tmp/json"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "gclient sync",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@json.output@{@@@",
       "@@@STEP_LOG_LINE@json.output@  \"solutions\": {@@@",
       "@@@STEP_LOG_LINE@json.output@    \"src-internal/\": {@@@",
       "@@@STEP_LOG_LINE@json.output@      \"revision\": 274229@@@",
       "@@@STEP_LOG_LINE@json.output@    }, @@@",
       "@@@STEP_LOG_LINE@json.output@    \"src/\": {@@@",
       "@@@STEP_LOG_LINE@json.output@      \"revision\": 170242@@@",
       "@@@STEP_LOG_LINE@json.output@    }@@@",
       "@@@STEP_LOG_LINE@json.output@  }@@@",
       "@@@STEP_LOG_LINE@json.output@}@@@",
       "@@@STEP_LOG_END@json.output@@@",
       "@@@STEP_LINK@170242@https://github.com/google/syzygy/commit/170242@@@",
       "@@@SET_BUILD_PROPERTY@got_revision@170242@@@"
     ]
   },
   {
     "cmd": [
       "python",
       "-u",
       "[DEPOT_TOOLS]\\gclient.py",
       "runhooks"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "env": {
       "GYP_DEFINES": "target_arch=ia32",
       "GYP_GENERATORS": "msvs",
       "GYP_MSVS_VERSION": "2013"
     },
     "name": "gclient runhooks"
   },
   {
     "cmd": [
       "python",
       "-u",
       "[BUILD]\\scripts\\slave\\compile.py",
       "--target",
       "Coverage",
       "--src-dir",
       "[SLAVE_BUILD]\\src",
       "--build-tool",
       "vs",
       "--solution",
       "[SLAVE_BUILD]\\src\\syzygy\\syzygy.sln",
       "--project",
       "build_all"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "compile"
   },
   {
     "cmd": [
       "python",
       "-u",
       "[SLAVE_BUILD]\\src\\syzygy\\build\\generate_coverage.py",
       "--verbose",
       "--syzygy",
       "--build-dir",
       "[SLAVE_BUILD]\\src\\build\\Coverage"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "capture_unittest_coverage"
   },
   {
     "cmd": [
       "python",
       "-u",
       "[BUILD]\\scripts\\slave\\syzygy\\gsutil_cp_dir.py",
       "[SLAVE_BUILD]\\src\\build\\Coverage\\cov",
       "gs://syzygy-archive/builds/coverage/170242"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "archive_coverage",
     "~followup_annotations": [
       "@@@STEP_LINK@coverage_report@https://syzygy-archive.commondatastorage.googleapis.com/builds/coverage/170242/index.html@@@"
     ]
   }
 ]