The installation of OpenShift 4, using the agent-based install, fails in a disconnected environment due to the lack of valid NTP sources

Issue

• During the installation, only 1 host achieves the ready state. The other 2 hosts are not being validated. The network is well configured and it works.

• The installation fails and shows the following errors:

  ...
  level=warning msg=Cluster validation: Hosts' clocks are not synchronized (there's more than a 4 minutes gap between clocks), please configure an NTP server via DHCP or set clocks manually.
  level=warning msg=Host node.dummy.hostname validation: Host couldn't synchronize with any NTP server
  ...