Increase min-ready for ubuntu-trusty
Increase min-ready for ubuntu-trusty

We're putting more jobs on ubuntu-trusty, increase min-ready from 1 to 4
to have more images available.

Once the conversion is done, we need to reduce bare-trusty min-ready.

Change-Id: Id287c49aa182b525b40e6b97bc59ed17e61c1a8a

noorul/os-project-config,Tesora/tesora-project-config,openstack-infra/project-config,noorul/os-project-config,Tesora/tesora-project-config,openstack-infra/project-config,dongwenjuan/project-config,dongwenjuan/project-config