Set WebRTC-VP8ConferenceTemporalLayers to 2 in tests

Bug: 1000023
Change-Id: I55d2f5134abb180f96cb9216d0ea5dee9456216d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1793084
Commit-Queue: Erik Språng <sprang@chromium.org>
Auto-Submit: Erik Språng <sprang@chromium.org>
Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Cr-Commit-Position: refs/heads/master@{#694937}

testing/variations/fieldtrial_testing_config.json

@@ -6850,6 +6850,23 @@
             ]
         }
     ],
+    "WebRTC-VP8ConferenceTemporalLayers": [
+        {
+            "platforms": [
+                "windows",
+                "mac",
+                "chromeos",
+                "linux",
+                "ios",
+                "android"
+            ],
+            "experiments": [
+                {
+                    "name": "2_V1"
+                }
+            ]
+        }
+    ],
     "WebRTC-VideoRateControl": [
         {
             "platforms": [