[COOK-3492] Add tests for upstart on CentOS 6.

https://tickets.opscode.com/browse/COOK-3492

Because of how the minitest handler for Chef works, we've had to
resort to the uglier test construction used here.  Alternatively, we
could have inspected the state of the system directly.

For more information on the issue in minitest, see:

https://github.com/calavera/minitest-chef-handler/issues/66