Add recheck message to Zuul config.

Change-Id: I1dc2c2e811ecf8e72befaf71b94742771e905230
Reviewed-on: https://review.openstack.org/19843
Reviewed-by: Clark Boylan <clark.boylan@gmail.com>
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Approved: James E. Blair <corvus@inaugust.com>
Tested-by: Jenkins
Add support for 'recheck no bug'

Change-Id: I01f10fc41f9830671161c65a53d70e7ffd149c08
Reviewed-on: https://review.openstack.org/19868
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Reviewed-by: Monty Taylor <mordred@inaugust.com>
Approved: James E. Blair <corvus@inaugust.com>
Tested-by: Jenkins