nginx: unified indentation character and add additional config entry

nginx: unified indentation character and add additional config entry

The original configure file mixed tab and space
characters as indentation, so use 4 spaces as the
default indentation character.

Add /etc/nginx/conf.d/*.conf as nginx additional configure
files. Then we can add individual conf file for other http
applications without modify the main nginx configure file.

Signed-off-by: James Qian <sotux82@gmail.com>