clear active shards when reloading default shard
clear active shards when reloading default shard

prevents zombie shards from hanging around

Change-Id: Iaf6109fb6997ef92e36146a4b1d4881a59d5c39c
Reviewed-on: https://gerrit.instructure.com/31584
Tested-by: Jenkins <d95b56ce41a2e1ac4cecdd398defd7414407cc08@instructure.com>
Reviewed-by: James Williams  <3a5f4ed991dbfa5c9ef76ad729d240ca12f62180@instructure.com>
Product-Review: Cody Cutrer <c4fe2b1d90ef8f2548c8aeabfa633434316f0305@instructure.com>
QA-Review: Cody Cutrer <c4fe2b1d90ef8f2548c8aeabfa633434316f0305@instructure.com>

instructure/switchman,ccutrer/switchman,krrg/switchman,instructure/switchman