Add variables for /root and /var, and change the defaults to be larger

Udate the preseed template and define to:
a) update the default sizes:
  /root: 32GB
  /var: 128GB
b) allow for upstream parameterization
 in the cobbler-node.pp file, you can now add:
  $root_part_size => "65536",
  $var_part_size => "1048576",
Which would make for a 64GB root and a 1TB /var partition