(Re)move preamble processing. Now in Vcloud::Launcher::Preamble.

configure_guest_customization_section now just takes a single
pre-templated/pre-processed script that will be passed to Fog.
Merge pull request #90 from bazbremner/move_preamble_processing

[#66849308] (Re)move preamble processing. Now in Vcloud::Launcher::Preamble.