Add google_compute_engine and boto py wheels to src's root .vpython

Bug: 781413
Change-Id: I6560282e0d0e228da9a1bb48f04977408d7635a0
Reviewed-on: https://chromium-review.googlesource.com/767292Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Reviewed-by: Robbie Iannucci <iannucci@chromium.org>
Commit-Queue: Benjamin Pastene <bpastene@chromium.org>
Cr-Commit-Position: refs/heads/master@{#516345}

.vpython

@@ -87,3 +87,14 @@ wheel: <
     platform: "win_amd64"
   >
 >
+
+# Used by:
+#   tools/perf/fetch_benchmark_deps.py
+wheel: <
+  name: "infra/python/wheels/google_compute_engine-py2_py3"
+  version: "version:2.6.2"
+>
+wheel: <
+  name: "infra/python/wheels/boto-py2_py3"
+  version: "version:2.48.0"
+>