[autotest] Manage shards with atest

This adds functionality to list, create and delete shards to atest.

BUG=None
TEST=Ran suites, manual test of create/list/delete.

Change-Id: I0771d0c1b46c7c6890819822204f42ac2211b104
Reviewed-on: https://chromium-review.googlesource.com/218295
Tested-by: Jakob Jülich <jakobjuelich@chromium.org>
Reviewed-by: Prashanth B <beeps@chromium.org>
Commit-Queue: Jakob Jülich <jakobjuelich@chromium.org>
5 files changed