[PPML] Upgrading Spark to 3.1.2 in Spark K8S example with occlum

[qiyuangong]

Ant found Driver pod exit issue with Spark 3.0.0. Need to upgrade to 3.1.2

• [x] Rebuild Spark spark-network-common with @qiuxin2012 's patch (https://github.com/qiuxin2012/spark/commit/b28afb0842cbe5d54238779b4cfedb4f1ff847de). Upload this jar to az download site.
• [x] Modify Dockerfile and README in https://github.com/intel-analytics/analytics-zoo/tree/master/ppml/trusted-big-data-ml/scala/docker-occlum/kubernetes

[ManfeiBai]

Get, start to working, sorry, my computer has restarted this morning and my Teams does not work fully without input inforation today

[qiyuangong]

Addressed by intel-analytics/analytics-zoo#4860 Issue closed