For me, I only had this problem on 1 of the 4 hosts in my cluster.
Here is what I did:
# imgbase layout
result was "ovirt-node-ng-4.2.6.1-0.20180913.0"
# imgbase base --remove ovirt-node-ng-4.2.6.1-0.20180913.0
(used to remove the "failed" 4.2.6.1 update)
# yum reinstall ovirt-node-ng-image-update.noarch
(used to re-install 4.2.6.1)
Now the host is updated to 4.2.6.1