Installation fails when resolvconf already has >=3 nameserver

The make script adds a nameserver to /etc/resolvconf/resolv.conf.d/head on the head node.

I already had 3 entries in there. My companies DNS server, Google's main one, and Google's backup one. When the internal CORD one was added, that brought the total to 4.

resolvconf silently fails if it's given a list of more than 3 nameservers. This is the fault of resolvconf. However given that we now know this, I think that Ansible should check whether (after adding a nameserver) resolvconf has >=4 nameservers. If so, it should fail and throw an error message telling the user to remove one of the nameservers.