Switch cros_download_vm DEPS hook to use gclient tuple support.

Slightly cleaner this way.

Bug: 947531
Change-Id: I9dcc66d92562ddae8adcbf58b7e0bf9a2ffdc481
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1625812Reviewed-by: John Budorick <jbudorick@chromium.org>
Commit-Queue: Ben Pastene <bpastene@chromium.org>
Cr-Commit-Position: refs/heads/master@{#663149}

DEPS

@@ -106,7 +106,7 @@ vars = {
   'checkout_simplechrome': '(checkout_chromeos and host_os == "linux") and ("{cros_board}" != "")',
   # Surround the board var in quotes so gclient doesn't try parsing the string
   # as an expression.
-  'cros_download_vm': '("{cros_board}" == "amd64-generic") or ("{cros_board}" == "betty")',
+  'cros_download_vm': '"{cros_board}" in ("amd64-generic", "betty")',
   # Should we build and test for public (ie: full) CrOS images, or private
   # (ie: release) images.
   'use_public_cros_config': 'not checkout_src_internal',