Workaround for Installing OKD 3.11

[eliu]

This is originally an issue from openshift-ansible due to centos repo frozen for 7.6. Please check out the following links about this disccussion:

• https://lists.openshift.redhat.com/openshift-archives/dev/2018-November/msg00005.html
• https://github.com/openshift/openshift-ansible/issues/7794
• https://github.com/vorburger/opendaylight-coe-kubernetes-openshift/issues/3
• https://github.com/openshift/openshift-ansible/issues/10564

I have already applied a temporary fix for that:

https://github.com/eliu/openshift-vagrant/blob/ad01aae4be9d193bbb5510760f3353f891011fd9/Vagrantfile#L66-L68