Nginx log reconfiguration

* sends logs to /mnt/logs/nginx instead of /var/log. Note that on fresh
  server startup, nginx will still log to /var/log until it reads its
  configuration.
* Installs logrotate configuration for freshly moved nginx logs
* Some directory and file permissions fixups
* Improved order of operations on nginx installation/bringup
Merge pull request #59 from edx/feature/jrbl/logging_nginx

Nginx log reconfiguration