Create manifest files to apply

When applying puppet manifests with `puppet apply` beaker will generate
the manifest code and send it to `stdin`. This is troublesome for
debugging as the actual code is never shown and hard to replicate.

This commit causes the manifest code to be stored in a `.pp` file in
`/tmp` and apply that file so that it may be viewed and reused when
debugging. This is similar to how rspec-system does it.