(maint) Use `copy_module_to` in `beaker_helper.rb`

Previously we were using `puppet_module_install()`. Which was ported from
Beaker-RSpec. Unfortunately for our heros that method has been refactored
since this was ran last. The method `puppet_module_install()` in Beaker
installs from the public forge, while the previous behavior, installing via
scp from the current directory, has moved to the method `copy_module_to`.
This updates the helper for the beaker tests to use the updated method.