Problem using mkimage-yum.sh skript

Inside the Moby project I’m trying to use the mentioned skript to generate an CentOS 7 Docker Image using sh mkimage-yum.sh -p “openssh-server net-tool bash-completion openssh openssh-clients” newimage-co7. But when this allmost comes to the end, the following message occurs: Kein Paket openssh-server net-tool bash-completion openssh openssh-clients verfügbar. (no package openssh-server net-tool bash-completion openssh openssh-clients availible).
My CentOS7 system is CentOS 7 Build 1708, Kernel 3.10.0-693.5.2.el7.x86_64. Any ideas for a solution?