Use the libmodulemd API properly when setting values on existing objects
    
    MBS has been using the libmodulemd API incorrectly by assuming that
    methods like `get_rpm_components` return the actual object in memory
    and not a copy. This has been true but wasn't something sgallagh
    intended. We found this out after he had me test his new version of
    libmodulemd. This PR removes those assumptions.