The docker service fails to start:

# systemctl start docker.service
Failed to start docker.service: Unit not found.

This is because docker.service has a dependency on a non-existent unit:

[Unit]
...
Requires=rhel-push-plugin.socket

The centos 7 extras package has removed it, as well as
'--authorization-plugin=rhel-push-plugin'.
See the c7-extras branch of https://git.centos.org/summary/rpms!docker
for any other changes.

-- 
Orion Poplawski
Technical Manager                          720-772-5637
NWRA, Boulder/CoRA Office             FAX: 303-415-9702
3380 Mitchell Lane                       [log in to unmask]
Boulder, CO 80301                   http://www.nwra.com