Move systest.rb to bin directory

Without this change you could install the puppet-acceptance code from
the git repo as a gem (via bundler), but could not run the systest.rb
program. This moves systest.rb to the bin directory, leaves a stub
behind, and drops the .rb extension (just 'cuz).
Merge pull request #430 from zaphod42/allow_execute_from_gem

Move systest.rb to bin directory