Refactoring Windows 2012r2 to use base task

Several files, including wimboot, were duplicated between
the core Windows task and the 2012r2 task. This refactors
the 2012r2 task to reference the base files. Consequently,
this adds broker execution to the 2012r2 task's
second-stage.ps1.erb, which is intended.

For https://tickets.puppetlabs.com/browse/RAZOR-413
Use wimboot 2.4.0

This updates the packaged wimboot file from 1.0.3 to 2.4.0 to
resolve occasional issues around bootmgr.exe extraction and
frozen install progress.

Fixes https://tickets.puppetlabs.com/browse/RAZOR-413