hosts: Update mtrcs0 FQDN

I moved the metrics Pi from the red network to the blue network.  I
started to get uncormfortable with the firewall changes that were
required to host a service on the red network.  I think it makes the
most sense to define the red network as egress only.

certs/nginx/mtrcs0.pyrocufflink.blue/server.cer

@@ -0,0 +1 @@
+../../lego/_.pyrocufflink.net.crt