Fix Debian service detection

* check_enabled now understands upstart (enough to
  check whether services start on boot)

* check_running now properly uses /usr/sbin/service
Resolve issue #130

* Modified spec/debian/commands_spec.rb to check for new commands
* Changed absolute paths to relative because #129
Merge pull request #130 from cs-travis/fix-debian-service-detection

Fix Debian service detection