refactor to make shard selection and parallel arguments public
refactor to make shard selection and parallel arguments public

Change-Id: I9bfc4495c0a1d49386f26ed9f509295791b9283d
Reviewed-on: https://gerrit.instructure.com/65359
Reviewed-by: Rob Orton <7e09c9d3e96378bf549fc283fd6e1e5b7014cc33@instructure.com>
Tested-by: Jenkins
Product-Review: Cody Cutrer <c4fe2b1d90ef8f2548c8aeabfa633434316f0305@instructure.com>
QA-Review: Cody Cutrer <c4fe2b1d90ef8f2548c8aeabfa633434316f0305@instructure.com>

instructure/switchman,instructure/switchman