CI/CD checks that run their setup start jobs immediately

When a check runs its setup (its key has no warm snapshot yet), its first job now starts on that set-up machine as soon as the setup ends. Before, the machine was deleted once it was copied, and every job waited for machines started from the copy, which only one server held: when that server was full, a check could wait minutes with no job running. Machines for the rest of its work still start from the copy.