webrtc: use correct cwd for running tests

scripts/slave/recipes/webrtc/standalone.expected/tryserver_webrtc_linux_memcheck.json

Index: scripts/slave/recipes/webrtc/standalone.expected/tryserver_webrtc_linux_memcheck.json
diff --git a/scripts/slave/recipes/webrtc/standalone.expected/tryserver_webrtc_linux_memcheck.json b/scripts/slave/recipes/webrtc/standalone.expected/tryserver_webrtc_linux_memcheck.json
index 3dd5f3c80078ddf5ae161fcbefb99f972c3279eb..88d6954312508b0446261f8fc0963baeecaa34d9 100644
--- a/scripts/slave/recipes/webrtc/standalone.expected/tryserver_webrtc_linux_memcheck.json
+++ b/scripts/slave/recipes/webrtc/standalone.expected/tryserver_webrtc_linux_memcheck.json
@@ -268,6 +268,7 @@
       "--tool",
       "memcheck"
     ],
+    "cwd": "[BUILDER_CACHE]/linux_memcheck",
     "name": "audio_decoder_unittests"
   },
   {
@@ -299,6 +300,7 @@
       "--tool",
       "memcheck"
     ],
+    "cwd": "[BUILDER_CACHE]/linux_memcheck",
     "name": "common_audio_unittests"
   },
   {
@@ -330,6 +332,7 @@
       "--tool",
       "memcheck"
     ],
+    "cwd": "[BUILDER_CACHE]/linux_memcheck",
     "name": "common_video_unittests"
   },
   {
@@ -361,6 +364,7 @@
       "--tool",
       "memcheck"
     ],
+    "cwd": "[BUILDER_CACHE]/linux_memcheck",
     "name": "modules_tests"
   },
   {
@@ -392,6 +396,7 @@
       "--tool",
       "memcheck"
     ],
+    "cwd": "[BUILDER_CACHE]/linux_memcheck",
     "name": "modules_unittests"
   },
   {
@@ -423,6 +428,7 @@
       "--tool",
       "memcheck"
     ],
+    "cwd": "[BUILDER_CACHE]/linux_memcheck",
     "name": "peerconnection_unittests"
   },
   {
@@ -454,6 +460,7 @@
       "--tool",
       "memcheck"
     ],
+    "cwd": "[BUILDER_CACHE]/linux_memcheck",
     "name": "rtc_media_unittests"
   },
   {
@@ -485,6 +492,7 @@
       "--tool",
       "memcheck"
     ],
+    "cwd": "[BUILDER_CACHE]/linux_memcheck",
     "name": "rtc_pc_unittests"
   },
   {
@@ -516,6 +524,7 @@
       "--tool",
       "memcheck"
     ],
+    "cwd": "[BUILDER_CACHE]/linux_memcheck",
     "name": "rtc_unittests"
   },
   {
@@ -547,6 +556,7 @@
       "--tool",
       "memcheck"
     ],
+    "cwd": "[BUILDER_CACHE]/linux_memcheck",
     "name": "system_wrappers_unittests"
   },
   {
@@ -578,6 +588,7 @@
       "--tool",
       "memcheck"
     ],
+    "cwd": "[BUILDER_CACHE]/linux_memcheck",
     "name": "test_support_unittests"
   },
   {
@@ -609,6 +620,7 @@
       "--tool",
       "memcheck"
     ],
+    "cwd": "[BUILDER_CACHE]/linux_memcheck",
     "name": "tools_unittests"
   },
   {
@@ -640,6 +652,7 @@
       "--tool",
       "memcheck"
     ],
+    "cwd": "[BUILDER_CACHE]/linux_memcheck",
     "name": "video_engine_tests"
   },
   {
@@ -671,6 +684,7 @@
       "--tool",
       "memcheck"
     ],
+    "cwd": "[BUILDER_CACHE]/linux_memcheck",
     "name": "voice_engine_unittests"
   },
   {
@@ -702,6 +716,7 @@
       "--tool",
       "memcheck"
     ],
+    "cwd": "[BUILDER_CACHE]/linux_memcheck",
     "name": "xmllite_xmpp_unittests"
   },
   {
@@ -733,6 +748,7 @@
       "--tool",
       "memcheck"
     ],
+    "cwd": "[BUILDER_CACHE]/linux_memcheck",
     "name": "webrtc_nonparallel_tests"
   },
   {