Always use version.
Don't download dirty RPMs.

The buildserver doesn't build dirty RPMs so don't try to download them.
We check this here, rather than in `admin/build-vagrant-box`, since the
`Vagrantfile`s may be changed.
Fix TOPLEVEL calculation in admin/_preamble.py.
Factor out vagrant into a module.
Add some tests.
Pass build server in to bootstrap.py.
Handle version via options.
Allow specifying build server.
Update documents to use new options.
Don't install admin.
setuptools.setup.find_packages' exclude argument takes a tuple.
bootstrap.sh takes *4* arguments now.
Merge forward.
Add comments to bootstrap.py.
Fix build-server handling.

Different bits of code expected a URL vs. a hostname.
twisted.python.usage doesn't allow taking over --version.
Update the right box (i.e. the base of the one we are bulding).
Specify a default buildserver.
Actually add the tests.
Fix for s/--version/--flocker-version/.