fuchsia: Update tools/fuchsia/local-sdk.py for SDK build changes

--product=product/sdk_image.gni is required by fx build now.

Change-Id: Ib91f211551bed08b7ff635ee0787c7ca2bf8dc8e
Reviewed-on: https://chromium-review.googlesource.com/c/1493087
Commit-Queue: Scott Graham <scottmg@chromium.org>
Commit-Queue: Wez <wez@chromium.org>
Auto-Submit: Scott Graham <scottmg@chromium.org>
Reviewed-by: Wez <wez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#636227}

tools/fuchsia/local-sdk.py

@@ -35,7 +35,8 @@ def BuildForArch(arch):
   build_dir = 'out/release-' + arch
   Run('scripts/fx', 'set', arch,
       '--packages=topaz/packages/sdk/topaz',
-      '--args=is_debug=false', '--args=build_sdk_archives=true', build_dir)
+      '--args=is_debug=false', '--args=build_sdk_archives=true',
+      '--product=products/sdk_image.gni', build_dir)
   Run('scripts/fx', 'full-build')