init: Fix upstart script for Centos6 (and Amazon Linux) (#1914)

dist/init/linux-upstart/caddy.conf.centos-6

@@ -3,19 +3,11 @@ description "Caddy HTTP/2 web server"
 start on runlevel [2345]
 stop on runlevel [016]
 
-# centos 6 upstart version does not support console
-console log
-
-# centos 6 upstart version does not support setuid/setgid
-setuid www-data
-setgid www-data
+console output
 
 respawn
 respawn limit 10 5
 
-# centos 6 upstart version does not support reload
-reload signal SIGUSR1
-
 # Let's Encrypt certificates will be written to this directory.
 env CADDYPATH=/etc/ssl/caddy
 
@@ -24,5 +16,6 @@ limit nofile 1048576 1048576
 script
         cd /etc/ssl/caddy
         rootdir="$(mktemp -d -t "caddy-run.XXXXXX")"
-        exec /usr/local/bin/caddy -agree -log=stdout -conf=/etc/caddy/Caddyfile -root=$rootdir
+        chown www-data:www-data $rootdir
+        exec sudo -u www-data /usr/local/bin/caddy -agree -log=/var/log/caddy.log -conf=/etc/caddy/Caddyfile -root=$rootdir
 end script