WebRTC: Update to new machines after a->b lab move.

masters/master.chromium.webrtc/slaves.cfg

Index: masters/master.chromium.webrtc/slaves.cfg
diff --git a/masters/master.chromium.webrtc/slaves.cfg b/masters/master.chromium.webrtc/slaves.cfg
index 29c4b4bcff632913542c69c27a76deba29dc35e8..b19beb7e4ddc7d92c11195f37cce66a6dd27a98c 100644
--- a/masters/master.chromium.webrtc/slaves.cfg
+++ b/masters/master.chromium.webrtc/slaves.cfg
@@ -52,7 +52,7 @@ slaves = [
     'version': 'win7',
     'bits': '64',
     'builder': ['Win7 Tester'],
-    'hostname': 'build130-a1',
+    'hostname': 'build99-b1',
   },
   {
     'master': 'ChromiumWebRTC',
@@ -60,7 +60,7 @@ slaves = [
     'version': 'win8',
     'bits': '64',
     'builder': ['Win8 Tester'],
-    'hostname': 'build56-a1',
+    'hostname': 'build97-b1',
   },
   {
     'master': 'ChromiumWebRTC',
@@ -68,6 +68,6 @@ slaves = [
     'version': 'win10',
     'bits': '64',
     'builder': ['Win10 Tester'],
-    'hostname': 'build2-a1',
+    'hostname': 'build95-b1',
   },
 ]