cockpit-machine-ovirt is part of cockpit >= 165 which is not in RHEL 7.5 and CentOS 7.5.1804 and won't be. So we need to rebuild cockpit within Virt SIG for providing it.
build available for testing at http://cbs.centos.org/koji/buildinfo?buildID=22693
can you please give it a run enabling centos cr repo as well?
As a side note, Fedora already includes full built cockpit so no need to provide cockpit-machine-ovirt in a separate repo.
The cockpit-machines-ovirt-165-2.el7 verified from the centos-ovirt-common-testing (http://cbs.centos.org/repos/virt7-ovirt-common-testing/), works as expected.
Found side issue (not affecting scope of this BZ) when updating cockpit-storaged-148 (in extras) to cockpit-storaged-165 (centos-ovirt-common-testing): missing udisks2 >= 2.6 package.
udisks2-2.7.3 is available in http://mirror.centos.org/centos/7/cr/x86_64/Packages/
cockpit-machines-ovirt landed in CentOS 7.5 / oVirt 4.2.