Require dnf-utils when installig on Fedora

[gbenhaim]

We currently require yum-utils which is wrong.
The change should be done in the lago-ovirt.spec.in

[mykaul]

This is not enough - you need to run 'dnf reposync' and then the command is slightly different (at least on F29) - it does not accept the same command args as the old reposync did :(