* [HUDI-1989] Refactor clustering tests for MoR table * refactor assertion helper * add CheckedFunction * SparkClientFunctionalTestHarness.java * put back original test case * move testcases out from TestHoodieMergeOnReadTable.java * add TestHoodieSparkMergeOnReadTableRollback.java * use SparkClientFunctionalTestHarness * add tag