refactor --for BaseEncoderTest

1)for function  
                 --EncodeFile(...)
                 --EncodeStream(...)
                 --InitWithPara(...)
    -- used SEncParamExt* pEncParamExt instead of " EUsageType usageType, int width ...."
     it will be more flexible for adding more parameters in test case such as thread num, temp layer num etc.
2) change some code and let it be more google style