Created playbook for disabling selinux

Disable SELinux:

*  Created a new playbook for managing SELinux configuration
*  `main.yml` includes the selinux playbook when SELinux is not disabled 

Based on: https://github.com/scollazo/dxs/commit/bbfe911dac8df8c73b565dd1a5f171433c8a0aab