[cproto] Update discovery file output.
[cproto] Update discovery file output.

Change-Id: Icce400e5430b1197eef3f29ec21a6e5139840c49
Reviewed-on: https://chromium-review.googlesource.com/1180648
Reviewed-by: Nodir Turakulov <ef4933a197ef7b4b3f55f1bec4942aead3637a2a@chromium.org>
Commit-Queue: Joanna Wang <bc6dfeb40460aa87d922e00661e02afbab58c45b@chromium.org>

luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go