【feature】mystreamer支持upstream和downstream使用不同的存储引擎

[blackghost-01]

数据迁移过程中（例如历史数据归档），源库和目标库希望使用不同的存储引擎（比如tokudb或者myrocks），达到数据压缩等目的。所以就需要在导入时，支持指定存储引擎类型，或者导出时忽略存储引擎选项（目标库有设置选定的默认存储引擎）

[BohuTANG]

Hi @blackghost-01 ,

From the mystreamer side, we should to parse the table schema and change the ENGINE option to TokuDB/MyRocks or others, so we think this issue priority is lower.

As you said, we can do that by setting the default engine. Thanks.

[blackghost-01]

期待实现

[BohuTANG]

@blackghost-01

This feature is done, the commit id is here: https://github.com/XeLabs/go-mydumper/commit/a0ee86efcbf1a7e2a3804c90c0370c188892a06f

Now, we can use the flage '--2engine=tokudb' to replace the upstream engine.

  -2engine string
        Downstream table engine

[blackghost-01]

great job