DzMehedi It seems you haven't installed the WordPress properly.
The beginning of the logs starts as:
2016/09/08 00:47:56 [error] 30669#0: *111 FastCGI sent in stderr: "PHP message: WordPress database error Unknown column 'dz_' in 'field list' for query SELECT dz_" while reading response header from upstream, client: xxxxxxx, server: dzmehedi.com, request: "POST /wp-admin/setup-config.php?step=2 HTTP/1.1", upstream: "fastcgi://unix:/var/run/php5-fpm.sock:", host: "dzmehedi.com", referrer: "http://dzmehedi.com/wp-admin/setup-config.php?step=1"
Let's ignore that part, since I assume you were configuring the installation.
You still seem have mis-configuration on your WordPress setup:
2016/09/09 10:46:55 [error] 737#0: *258650 connect() to unix:/var/run/php5-fpm.sock failed (11: Resource temporarily unavailable) while connecting to upstream, client: xxx.xxx.xxx.x, server: dzmehedi.com, request: "POST /xmlrpc.php HTTP/1.0", upstream: "fastcgi://unix:/var/run/php5-fpm.sock:", host: "xxxxxxx"
Resource temporarily unavailable is not something to easily ignore.
The 404 cannot be from your Nginx setup, this is directly related to the way you have installed WordPress application.
Do you get the 404 error often or it did happen only once ? That error might have been caused due to an automatic upgrade by WordPress itself.