[luciexe] Add extra responsibility to invoker in luciexe protocol
[luciexe] Add extra responsibility to invoker in luciexe protocol

Invoker now should set the status, create_time, start_time and reset
following fields in the initial build.
 * EndTime
 * Output
 * StatusDetails
 * Steps
 * SummaryMarkdown
 * Tags
 * UpdateTime

R=iannucci

Bug: 1119441
Change-Id: I37961613fdc2596ef650841503489baec564fb4d
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/2377000
Commit-Queue: Robbie Iannucci <40f3d43a28ebae3cb819288542e1c84d73d962d5@chromium.org>
Reviewed-by: Prathmesh Prabhu <6bd99e63707dfb9648154f5b1933c36b73b63d70@google.com>
Reviewed-by: Robbie Iannucci <40f3d43a28ebae3cb819288542e1c84d73d962d5@chromium.org>
Auto-Submit: Yiwei Zhang <50b2a565e2e78c292794832469a30ce5abc9959c@google.com>

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