Permit bug numbers in rechecks.
Permit bug numbers in rechecks.

But do not require them.
Also, retrigger the silent pipeline on rechecks.

Change-Id: I83d6ef44e0e37cb89204d02cd4e5b1fabc47cec9
Reviewed-on: https://review.openstack.org/18443
Reviewed-by: Clark Boylan <635fc31d01fa593720982fa0568e87170cedbe2c@gmail.com>
Approved: Jeremy Stanley <98883b97e35b7bb1ac282bb863f2e9d917db0454@yuggoth.org>
Reviewed-by: Jeremy Stanley <98883b97e35b7bb1ac282bb863f2e9d917db0454@yuggoth.org>
Tested-by: Jenkins

openstack-infra/project-config,anbangr/osci-project-config,coolsvap/project-config,dongwenjuan/project-config,citrix-openstack/project-config,noorul/os-project-config,anbangr/osci-project-config,osrg/project-config,Tesora/tesora-project-config,citrix-openstack/project-config,open-switch/infra_project-config,dongwenjuan/project-config,coolsvap/project-config,noorul/os-project-config,osrg/project-config,openstack-infra/project-config,Tesora/tesora-project-config,open-switch/infra_project-config