ovirt-provider-ovn should be installed and configured during engine-setup.
Verified: 4.2.0-0.0.master.20170813134654.gitaee967b.el7.centos
This bugzilla is included in oVirt 4.2.0 release, published on Dec 20th 2017. Since the problem described in this bug report should be resolved in oVirt 4.2.0 release, published on Dec 20th 2017, it has been closed with a resolution of CURRENT RELEASE. If the solution does not work for you, please open a new bug report.