[swarming] reproduce: Add reproduce command.
[swarming] reproduce: Add reproduce command.

Bug:1188473
Change-Id: I3ec00a7452d8f4f508ddeb82a54902d20f9b1980
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/2888217
Commit-Queue: Joanna Wang <bc6dfeb40460aa87d922e00661e02afbab58c45b@chromium.org>
Auto-Submit: Joanna Wang <bc6dfeb40460aa87d922e00661e02afbab58c45b@chromium.org>
Reviewed-by: Takuto Ikuta <71927f930fca81015e0f496c65cd126ab1a692e3@chromium.org>
Reviewed-by: Junji Watanabe <aaef61ef98ffea505db831f310be2a0eb8492537@google.com>

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