Fix Bundler interfering with itself

Without this patch it's difficult to use the parent rake task to build
all of the packages because Bundler starts off and pollutes the
environment.  This environment pollution prevents the gem install
command from installing the bundler gem into the correct location.
Instead it installs into the bundle directory for the build.

This patch addresses the problem by wrapping Ruby installation commands
inside of Bundler.with_clean_env