Fix some issues in TestRMWebServicesCapacitySchedDynamicConfig

YARN-10512 introduced some changes that could be fixed, Peter Bacsko highlighted those issues with this comment.

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#1 In TestRMWebServicesCapacitySchedDynamicConfig:

config.set(YarnConfiguration.SCHEDULER_CONFIGURATION_STORE_CLASS,
	        YarnConfiguration.MEMORY_CONFIGURATION_STORE);

This call is repeated multiple times, this could be set somewhere else.

#2 In TestRMWebServicesCapacitySchedDynamicConfig:

validateSchedulerInfo(json, "weight", "root.default", "root.test1", "root.test2");

"root.default", "root.test1" and "root.test2" are the same in all cases, you might want to drop them

#3 In TestRMWebServicesCapacitySchedDynamicConfig

          @Before
	  @Override
	  public void setUp() throws Exception {
	    super.setUp();
	  }

This method does nothing, can be removed.