[prpc] correct code->http status mapping
[prpc] correct code->http status mapping

Based on
https://cloud.google.com/apis/design/errors

R=9f116ddb1b24f6fc1916a676eb17161b6c07dfc1@chromium.org

Bug:
Change-Id: Ib2e0cae666ed1a0cc12d4c591f71f04c3fc75d69
Reviewed-on: https://chromium-review.googlesource.com/853227
Reviewed-by: Vadim Shtayura <9f116ddb1b24f6fc1916a676eb17161b6c07dfc1@chromium.org>
Commit-Queue: Nodir Turakulov <ef4933a197ef7b4b3f55f1bec4942aead3637a2a@chromium.org>

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