Install Varnish from epel repos

[onnimonni]

Currently we install varnish from custom rpm packages from: http://repo.varnish-cache.org/.

This causes problems when we try to update the varnish package.

We should use epel repos instead like this tutorial shows here:
https://devops.profitbricks.com/tutorials/install-and-configure-varnish-with-apache-on-centos-7/

[jcnventura]

This is now critical. The repo.varnish-cache.org site stopped working last Thursday.

[tharna]

Epel doesn't seem to have latest releases. We need to use official packagecloud repos instead.