Up the debian-jessie min-ready
Up the debian-jessie min-ready

This patch increases the min-ready nodes for Jessie from 1 to 3,
because otherwise, we have to wait for a really long time until
a build start. This can be blocking, especially when we are
waiting for a fix of a build-dependency.

Change-Id: I5888cd6b9d0aa67a99bf9d32e85cd18347542e68

openstack-infra/project-config,Tesora/tesora-project-config,openstack-infra/project-config,Tesora/tesora-project-config