improve clustering algorithm

Signed-off-by: Michal Toman <mtoman@redhat.com>
retrace: do not spawn task when package lob is missing

Signed-off-by: Michal Toman <mtoman@redhat.com>
retrace: do not fix UsrMove in the DB

Signed-off-by: Michal Toman <mtoman@redhat.com>