webrtc: use correct cwd for running tests

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

Index: scripts/slave/recipes/webrtc/standalone.expected/client_webrtc_linux_memcheck.json
diff --git a/scripts/slave/recipes/webrtc/standalone.expected/client_webrtc_linux_memcheck.json b/scripts/slave/recipes/webrtc/standalone.expected/client_webrtc_linux_memcheck.json
index ad23a34b613fd03c4e1c8d3b467dd67c08624d84..1b5bbbfe1298342ad1c2bb5c5c1e22b023854f27 100644
--- a/scripts/slave/recipes/webrtc/standalone.expected/client_webrtc_linux_memcheck.json
+++ b/scripts/slave/recipes/webrtc/standalone.expected/client_webrtc_linux_memcheck.json
@@ -260,6 +260,7 @@
       "--tool",
       "memcheck"
     ],
+    "cwd": "[BUILDER_CACHE]/Linux_Memcheck",
     "name": "audio_decoder_unittests"
   },
   {
@@ -291,6 +292,7 @@
       "--tool",
       "memcheck"
     ],
+    "cwd": "[BUILDER_CACHE]/Linux_Memcheck",
     "name": "common_audio_unittests"
   },
   {
@@ -322,6 +324,7 @@
       "--tool",
       "memcheck"
     ],
+    "cwd": "[BUILDER_CACHE]/Linux_Memcheck",
     "name": "common_video_unittests"
   },
   {
@@ -353,6 +356,7 @@
       "--tool",
       "memcheck"
     ],
+    "cwd": "[BUILDER_CACHE]/Linux_Memcheck",
     "name": "modules_tests"
   },
   {
@@ -384,6 +388,7 @@
       "--tool",
       "memcheck"
     ],
+    "cwd": "[BUILDER_CACHE]/Linux_Memcheck",
     "name": "modules_unittests"
   },
   {
@@ -415,6 +420,7 @@
       "--tool",
       "memcheck"
     ],
+    "cwd": "[BUILDER_CACHE]/Linux_Memcheck",
     "name": "peerconnection_unittests"
   },
   {
@@ -446,6 +452,7 @@
       "--tool",
       "memcheck"
     ],
+    "cwd": "[BUILDER_CACHE]/Linux_Memcheck",
     "name": "rtc_media_unittests"
   },
   {
@@ -477,6 +484,7 @@
       "--tool",
       "memcheck"
     ],
+    "cwd": "[BUILDER_CACHE]/Linux_Memcheck",
     "name": "rtc_pc_unittests"
   },
   {
@@ -508,6 +516,7 @@
       "--tool",
       "memcheck"
     ],
+    "cwd": "[BUILDER_CACHE]/Linux_Memcheck",
     "name": "rtc_unittests"
   },
   {
@@ -539,6 +548,7 @@
       "--tool",
       "memcheck"
     ],
+    "cwd": "[BUILDER_CACHE]/Linux_Memcheck",
     "name": "system_wrappers_unittests"
   },
   {
@@ -570,6 +580,7 @@
       "--tool",
       "memcheck"
     ],
+    "cwd": "[BUILDER_CACHE]/Linux_Memcheck",
     "name": "test_support_unittests"
   },
   {
@@ -601,6 +612,7 @@
       "--tool",
       "memcheck"
     ],
+    "cwd": "[BUILDER_CACHE]/Linux_Memcheck",
     "name": "tools_unittests"
   },
   {
@@ -632,6 +644,7 @@
       "--tool",
       "memcheck"
     ],
+    "cwd": "[BUILDER_CACHE]/Linux_Memcheck",
     "name": "video_engine_tests"
   },
   {
@@ -663,6 +676,7 @@
       "--tool",
       "memcheck"
     ],
+    "cwd": "[BUILDER_CACHE]/Linux_Memcheck",
     "name": "voice_engine_unittests"
   },
   {
@@ -694,6 +708,7 @@
       "--tool",
       "memcheck"
     ],
+    "cwd": "[BUILDER_CACHE]/Linux_Memcheck",
     "name": "xmllite_xmpp_unittests"
   },
   {
@@ -725,6 +740,7 @@
       "--tool",
       "memcheck"
     ],
+    "cwd": "[BUILDER_CACHE]/Linux_Memcheck",
     "name": "webrtc_nonparallel_tests"
   },
   {