[Improvement] [tez]：Optimize user switch to shuffle mode local/remote.

[baitian77]

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• I have searched in the issues and found no similar issues.

What would you like to be improved?

Currently, users need to set the parameter tez.am.launch.launch.cmd-opts to switch between local shuffle and remote shuffle, but this parameter is difficult for users to understand.
We need a simpler and easier to understand parameter，such as tez.shuffle.mode = local/remote

How should we improve?

1. set tez.am.launch.launch.cmd-opts=-XX:+PrintGCDetails -verbose:gc -XX:+PrintGCTimeStamps -XX:+UseNUMA -XX:+UseParallelGC org.apache.tez.dag.app.RssDAGAppMaster。 【 note： this config will not change 】
2. add new conf tez.shuffle.mode which will used in RssDAGAppMaster. when this conf equal local, RssDAGAppMaster will use all DAGAppMaster functions

Are you willing to submit PR?

• Yes I am willing to submit a PR!

[roryqi]

Could we do similar things in another class? Maybe you can refer to DelegationRssShuffleManager in our project.