[JIRA] (OVIRT-1650) upgrade CentOS slaves to 7.4

upgrade CentOS slaves to 7.4 ---------------------------- Key: OVIRT-1650 URL: https://ovirt-jira.atlassian.net/browse/OVIRT-1650 Project: oVirt - virtualization made easy Issue Type: Improvement Reporter: Evgheni Dereveanchin Assignee: Evgheni Dereveanchin Priority: High CentOS 7.4 is out and internal mirrors are in sync. We should start upgrading to this version to ensure CI works properly with new VDSM patches expecting updated versions of libvirt.