Purpose of this pull request

Fix the issue of throwing connection cast-exception when use greenplum-writer.

Which issue you fix

Fixes # (1119).

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并没有修复啊，还是包类型转换错误Caused by: java.lang.ClassCastException: com.pivotal.jdbc.greenplumbase.ddu cannot be cast to org.postgresql.core.BaseConnection，greenplum的版本：5.21.0

只要是greenplum作为目标端的都报驱动找不到，但是只有gp到gp的就可以，怀疑是源端的gp是能加载进来的，导致目标的不加载也能运行

只要是greenplum作为目标端的都报驱动找不到，但是只有gp到gp的就可以，怀疑是源端的gp是能加载进来的，导致目标的不加载也能运行
是什么模式下运行的呢，方便贴一下脚本么