Fedora 20 is not supported any more on master

[Nir Soffer]

Hi infra,

Please disable the fedora 20 jobs [1] for vdsm master. This job is relevant only
for ovirt-3.5 branch.

Fedora 20 will be EOL at a about a month, and we require now libvirt version
which is not available even on Fedora 20 virt-preview [2].

[1] http://jenkins.ovirt.org/job/vdsm_master_install-rpm-sanity-fc20_created/1527
[2] https://gerrit.ovirt.org/40069

Thanks,
Nir