FreeRADIUS integration

For now, clients.conf (NAS) can be integrated into a database table and 
we added necessary info in switches.conf so that it can be populated by PacketFence.

== Requirements ==
 * freeradius2-mysql package installed

== Installation instructions ==
 * Create database table radius_nas:
  mysql -u root -p pf -v < addons/freeradius-integration/freeradius-nas-table.sql

 * FreeRADIUS config
  * uncomment "$INCLUDE sql.conf" (so that it is activated) under modules {...} in /etc/raddb/radiusd.conf
  * add "sql" under instantiate {...} in /etc/raddb/radiusd.conf
  * configure login, password, hostname, database name in /etc/raddb/sql.conf
  * uncomment "readclients = yes" (so that it is activated) in /etc/raddb/sql.conf
  * change nas_table to nas_table = "radius_nas" in /etc/raddb/sql.conf

 * PacketFence
  * You need to hook pf::freeradius::freeradius_populate_nas_config() somehow. It will populate the radius_nas table.
   For example, a new executable like below started by pacemaker would suffice:
#!/usr/bin/perl

use constant INSTALL_DIR => '/usr/local/pf';
use lib INSTALL_DIR . "/lib";

use pf::freeradius;

freeradius_populate_nas_config();

  * Make sure that freeradius is restarted everytime a new switch is added otherwise it won't be handled by FreeRADIUS
