Add "opencv" and "numpy" to vpython spec.

These packages were identified as optional Catapult packages,
along with the existing "psutil" using a codesearch for
"ImportOptionalModule".

BUG=chromium:762005
TEST=local
  - Loaded spec on Linux and Mac.

Change-Id: I4bb97d6f2251e3cc1db77691ed4c2f27f70b275e
Reviewed-on: https://chromium-review.googlesource.com/657959
Reviewed-by: Robbie Iannucci <iannucci@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Daniel Jacques <dnj@chromium.org>
Cr-Commit-Position: refs/heads/master@{#500697}

.vpython

@@ -30,3 +30,28 @@ wheel: <
   name: "infra/python/wheels/psutil/${platform}_${py_python}_${py_abi}"
   version: "version:5.2.2"
 >
+wheel: <
+  name: "infra/python/wheels/opencv_python/${platform}_${py_python}_${py_abi}"
+  version: "version:3.2.0.7"
+  match_tag: <
+    platform: "win32"
+  >
+  match_tag: <
+    platform: "win_amd64"
+  >
+  match_tag: <
+    abi: "cp27mu"
+    platform: "manylinux1_i686"
+  >
+  match_tag: <
+    abi: "cp27mu"
+    platform: "manylinux1_x86_64"
+  >
+  match_tag: <
+    platform: "macosx_10_6_intel"
+  >
+>
+wheel: <
+  name: "infra/python/wheels/numpy/${platform}_${py_python}_${py_abi}"
+  version: "version:1.12.1"
+>