(PUP-1802) Puppet agent should use ruby.exe directly

Currently when puppet runs as a service on Windows, it executes a batch script
in a cmd.exe process. This adds a layer of unnecessary complexity when we could
call our vendored ruby directly with the necessary arguments for the service to
run.

This switches over to using ruby.exe directly.
This may or may not have been necessary. When I passed it as `'somepath/along/this/way'` it threw errors, but it could have been due to the apostrophe usage instead of double quotes.