[SPARK-3124] Fix the jar version conflict in uber-jar

Both netty-3.2.2.Final.jar and netty-3.6.6.Final.jar are flatten into the assembly package, however, the class(NioWorker) signature difference leads to the failure in launching sparksql CLI/ThriftServer.

And also a tiny bug found in `CLISuite` & `HiveThriftServer2Suite` after fixing the duplicated netty jar.
When building against Hadoop-2.0.2, I found that only this dependency exclusion (not the additional one you included below) was necessary to get past the error you mentioned.