Added configuration for the specific modules

Hi,

The current version of the puppet-racktables has some specific apache/nginx packages installations. When using this module, it will conflict when the environment already has an apache or nginx puppet module. It will fail that package['x'] is already declared.

With this pull request, the "web_server.pp" file has been changed so it will call either the puppetlabs-apache module, or the jfryman-nginx module and use the specific 'vhost' defines.