(MCO-550) Use RubyW for Windows service

Previously, any powershell related functions (facter facts, providers, execs,
MCO triggered powershell commands) fail to return 0 properly, and therefore
fail, but only when triggered via the MCO daemon under windows.

Switching back to using rubyw now that bug #7239 was backported to Ruby
1.9.3 (https://bugs.ruby-lang.org/issues/9232). This allows us to take
advantage of using rubyw and providing proper exit codes for powershell
processes.