Change to thumbprint for certificates

This PR is required to make sure that we are associating the correct certificate to the IIS binding. We used to use certificate_name for this. During the heartbleed saga, we rekeyed our certificates. When we did this, we reinstalled the correct certificate. BUT IIS didnt realise that it had to change to use the new certificate as it used the name (both certs had the same friendly name)

Therefore using the thumbprint is the correct thing to do here