Continue fix for 9871
Continue fix for 9871

The existing logic was too tortured, and the previous fix was bad.
Rewrite to extract "get_statuses()" to a worker, and make it
extremely clear which VM hostkeys are being updated and why.

Signed-off-by: Dan Mick <b07550071eaa6a9296289c43bbd6c90559196431@redhat.com>

t-miyamae/teuthology,robbat2/teuthology,SUSE/teuthology,ceph/teuthology,dreamhost/teuthology,yghannam/teuthology,dreamhost/teuthology,caibo2014/teuthology,SUSE/teuthology,caibo2014/teuthology,dmick/teuthology,ivotron/teuthology,ceph/teuthology,ivotron/teuthology,tchaikov/teuthology,dmick/teuthology,robbat2/teuthology,yghannam/teuthology,zhouyuan/teuthology,ktdreyer/teuthology,ktdreyer/teuthology,SUSE/teuthology,michaelsevilla/teuthology,t-miyamae/teuthology,zhouyuan/teuthology,tchaikov/teuthology,michaelsevilla/teuthology,dmick/teuthology