Fix motd-carp-state.sh

The current release is not necessarily the first line of dmesg.boot

roles/post-install/files/motd-carp-state.sh

@@ -6,7 +6,7 @@ fi
 
 if [ ! -f /tmp/carp.state ]; then
     # Replace OpenBSD version in motd after each boot for it to be up to date after an upgrade
-    sed -i "1 s/^.*$/$(head -1 \/var\/run\/dmesg.boot)/" /etc/motd-original
+    sed -i "1 s/^.*$/$(grep OpenBSD \/var\/run\/dmesg.boot | tail -1)/" /etc/motd-original
     echo "unknown" > /tmp/carp.state
 fi