Allow content to be set via resouce name;

Now i can write many directives easy way.
For example:

sudo::directive { "pgpool ip addr add ${master_ip}":
   content => 'postgres ALL=(ALL) NOPASSWD: /sbin/ip addr add ${master_ip}/24 dev eth0':
   content => 'postgres ALL=(ALL) NOPASSWD: /sbin/ip addr del ${master_ip}/24 dev eth0':
   content => 'postgres ALL=(ALL) NOPASSWD: /sbin/arping':
}