skylab_test_runner: add input/output protos for test_runner Go program

I aim to replace almost all of the recipe with a luciexe-based program, and
these messages are the way that the recipe will initiate that program
and read any output. The program will write data to Buildbucket itself,
so all that really needs to go back to the recipe is the summary.

BUG=chromium:1165962
TEST=regen

Change-Id: I0d84f8e51e96a798551bba8fceaf08289c7cb10f
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/infra/proto/+/2651106
Reviewed-by: Prathmesh Prabhu <pprabhu@google.com>
Commit-Queue: Sean Abraham <seanabraham@chromium.org>
2 files changed