Small certificate hook updates

1. Preserve mode, owndership, timestamps when copying certificates.
   Ownership is updated after copying.
2. Reload dovecot on mail.lunch.org.uk.

states/certificates/dehydrated/hooks/deploy.sh

@@ -7,13 +7,14 @@ action=$1
 shift
 
 deploy_cert() {
-    cp -R /var/lib/dehydrated/certs/* /var/local/certificates/
+    cp -a /var/lib/dehydrated/certs/* /var/local/certificates/
     chown -R root:ssl-cert /var/local/certificates/
 
     DOMAIN="$1"
     case $DOMAIN in
         "mail.lunch.org.uk")
             systemctl restart exim4
+            systemctl reload dovecot
             ;;
     esac
 }