reworked php7.3 stack

* replace previous stack php7 variables
* properly set stack php = php7.2 and php73 = php7.3
* rename upstream php72 and php73 to avoid issues when migrating from EEv3
* use unix socket in nginx upstream instead of TCP/IP

wo/cli/templates/22222.mustache

@@ -39,6 +39,6 @@ server {
   location ~ \.php$ {
     try_files $uri =404;
     include fastcgi_params;
-    fastcgi_pass php;
+    fastcgi_pass php72;
   }
 }