In case anyone stumbles onto this having the same issue. Remove your docker-ee.repo file then regenerate it using yum-config-manager. If you don’t the, the 17.03 repos will still be there and won’t allow yum to see the upgrade path.
sudo rm /etc/yum.repos.d/docker-ee.rep
sudo yum-config-manager --add-repo <docker-ee-repo>
yum makecache fast
sudo yum upgrade -y
That should force yum to to pull in the next version.
Hope this helps!