Use MockRMMemoryStateStore to reduce test failures

Error Message

Stacktrace

java.lang.AssertionError: expected null, but was:<submit_time: 1471885197416 application_submission_context { application_id { id: 1 cluster_timestamp: 1471885197388 } application_name: "" queue: "default" priority { priority: 0 } am_container_spec { } cancel_tokens_when_complete: true maxAppAttempts: 2 resource { memory: 1024 virtual_cores: 1 } applicationType: "YARN" keep_containers_across_application_attempts: false attempt_failures_validity_interval: 0 am_container_resource_request { priority { priority: 0 } resource_name: "*" capability { memory: 1024 virtual_cores: 1 } num_containers: 0 relax_locality: true node_label_expression: "" execution_type_request { execution_type: GUARANTEED enforce_execution_type: false } } } user: "jenkins" start_time: 1471885197417 application_state: RMAPP_FINISHED finish_time: 1471885197478>
	at org.junit.Assert.fail(Assert.java:88)
	at org.junit.Assert.failNotNull(Assert.java:664)
	at org.junit.Assert.assertNull(Assert.java:646)
	at org.junit.Assert.assertNull(Assert.java:656)
	at org.apache.hadoop.yarn.server.resourcemanager.TestRMRestart.testFinishedAppRemovalAfterRMRestart(TestRMRestart.java:1656)