Clone of https://pagure.io/fedora-infrastructure/issue/6283.

Description:
registry.fedoraproject.org/fedora:latest should point to the latest version of Fedora base image, yet it points to F25 image instead.

Check using:
docker-1.13.1-28.gitb5e3294.fc27.x86_64

How to check:
1. docker pull registry.fedoraproject.org/fedora:latest
2. docker inspect registry.fedoraproject.org/fedora:latest

Expected result:
Config.Env should be set to F26 container

Actual result:

        "Config": {
            ...
            "Env": [
                "DISTTAG=f25container",
                "FGC=f25"
            ],
            ...