Add support for preseeding debconf

[tfoote]

The new nao-meshes require accepting a license. For automatied builds we can preseed the debconf to accept the license.

The process is documented here: https://serverfault.com/questions/407317/passing-default-answers-to-apt-get-package-install-questions/407358#407358

The nao settings look like this:

$ sudo debconf-get-selections | grep nao
ros-indigo-nao-meshes   ros-nao-meshes/present-ros-nao-meshes   note    
ros-indigo-nao-meshes   ros-nao-meshes/error-ros-nao-meshes error   
ros-indigo-nao-meshes   ros-nao-meshes/accepted-ros-nao-meshes  boolean true

This will probably need to be part of the bootstrap so that any job that depends on the nao_meshes can install it successfully non-interactively.