[components] Silence a useless exception.
[components] Silence a useless exception.

Thanks python. While at it, include a permanent workaround for
  AssertionError: No api proxy found for service "system"

Found through StackDriver exception reporting.

R=747cf52e0cef2e3e9371802a2d344b6c87126a4b@chromium.org

Change-Id: Ie051b506264dc25eb015d07bb4710cdfd8f9fcd7
Reviewed-on: https://chromium-review.googlesource.com/c/1384426
Reviewed-by: Quinten Yearsley <747cf52e0cef2e3e9371802a2d344b6c87126a4b@chromium.org>
Commit-Queue: Marc-Antoine Ruel <d2bf0fc09b08f7b0888b3ddab32b3e89c7122c8b@chromium.org>

luci/luci-py,luci/luci-py,luci/luci-py,luci/luci-py