Add new messages for product-scenario testing
    
    These messages can be used to represent a scenario
    of multiple products that is ready for testing and handle
    reporting test results against the product scenario.
    
    The following messages are being added:
    
     - product-scenario.build.complete
     - product-scenario.build.error
     - product-scenario.test.complete
     - product-scenario.test.error
    
    In the above messages, the {build} event means
    the product scenario is ready for testing and the
    {test} event means reporting test results for the
    product scenario execution.