Add `--no-content` argument to `create-repo`

Windows ISO extraction is a current known issue.
To subvert this issue, users can manually extract
the ISO and place it in the repo_store directory.
However, previous to this commit, users would
need to enter a stub iso-url to make the
repo's directory in the repo_store. This new
`--no-content` flag will allow the creation of a
repo without an iso-url or url so the repo_store
directory can be manually configured.

For https://tickets.puppetlabs.com/browse/RAZOR-361
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