Don't rely on LoadErrors in Parallel::TestBroker#load_sauce_config

The load_sauce_config method in lib/sauce/parallel/test_broker.rb is more complicated than it needs to be and doesn't even work. The following line doesn't do what it is supposed to:

    raise LoadError "Can't find sauce_helper, please add it in ./features/support/sauce_helper.rb"

It raises a NoMethodError since LoadError is not a method. The error it was supposed to raise would have been misleading anyway. That is the error that is supposed to be raised when none of the config files exist. It doesn't mean you need a ./features/support/sauce_helper.rb file.

I believe this simplifies the code and is closer to the behavior a user would want.