(PUP-1318) Stop squelching service output so that it's easier to diagnose service failures.

This closes pull request 2281.
Redmine 565, a seven year old issue referenced in a comment in lib/puppet/provider/service/service.rb, is no longer applicable to `Puppet::Util::Execution#execute`.  It was squelching service output because of a bug in ruby where `#read` on a pipe never returned when the spawned process is SIGTERM'd by one of its children.  The current implementation of `Puppet::Util::Execution#execute` redirects to a temporary file instead of reading from a pipe.
We should no longer be squelching service output so that users can easily diagnose service failures.