NGINX: issue with 'default' conf files on Centos

* NGINX: fixed issue with displaying "Welcome NGINX" page for some non ubuntu platforms.

  For example: 
  Centos use Nginx on EPEL, which populates /etc/nginx/conf.d/default.conf
  So, it will be loaded at first, because in bz-webserver/templates/default/nginx.conf.erb
  we have following lines:

  ```
    include /etc/nginx/conf.d/*.conf;
    include /etc/nginx/sites-enabled/*;
  ```