Simplify Centos Dockerfile for Molecule

Base the Centos image for molecule on official
CentOS systemd docker container.

Align the tagging policy with Centos images
on docker hub.

Change-Id: Ia2743ab78faed858dc5a7f3611cffb779b23d463
Issue-ID: OOM-1774
Signed-off-by:  Bartek Grzybowski <b.grzybowski@partner.samsung.com>
diff --git a/ansible/test/images/docker/centos7/Dockerfile b/ansible/test/images/docker/centos7/Dockerfile
index 8c024ab..289ee8c 100644
--- a/ansible/test/images/docker/centos7/Dockerfile
+++ b/ansible/test/images/docker/centos7/Dockerfile
@@ -1,29 +1,8 @@
-# https://github.com/chrismeyersfsu/provision_docker/tree/master/files
-FROM centos:centos7
-ENV container docker
-
-RUN yum -y update; yum clean all
-
-RUN systemctl mask dev-mqueue.mount dev-hugepages.mount \
-    systemd-remount-fs.service sys-kernel-config.mount \
-    sys-kernel-debug.mount sys-fs-fuse-connections.mount \
-    display-manager.service graphical.target systemd-logind.service
+FROM centos/systemd
 
 RUN yum -y install openssh-server sudo openssh-clients \
     epel-release python-docker-py iproute
-RUN sed -i 's/#PermitRootLogin no/PermitRootLogin yes/' /etc/ssh/sshd_config
-RUN ssh-keygen -q -f /etc/ssh/ssh_host_rsa_key -N '' -t rsa && \
-    ssh-keygen -q -f /etc/ssh/ssh_host_ecdsa_key -N '' -t ecdsa && \
-    ssh-keygen -q -f /etc/ssh/ssh_host_ed25519_key -N '' -t ed25519
-RUN echo 'root:docker.io' | chpasswd
 RUN systemctl enable sshd.service
-
-# firewalld needs this .. and I needs my firewalld
-ADD dbus.service /etc/systemd/system/dbus.service
-RUN systemctl enable dbus.service
-
-VOLUME ["/run"]
-
 EXPOSE 22
 
 CMD ["/usr/sbin/init"]