test/cluster_test: make TestRegionStatistics more stable (tikv#8320) #583

Job	Run time
chunks (1, Unit Test(1))	1m 33s
chunks (1, Unit Test(1))	5m 15s
chunks (2, Unit Test(2))	1m 31s
chunks (2, Unit Test(2))	5m 23s
chunks (3, Unit Test(3))	1m 33s
chunks (3, Unit Test(3))	5m 13s
chunks (4, Tests(1))	1m 31s
chunks (4, Tests(1))	5m 0s
chunks (5, Tests(2))	1m 32s
chunks (5, Tests(2))	5m 12s
chunks (6, Tools Test)	1m 31s
chunks (6, Tools Test)	5m 32s
chunks (7, Client Integration Test)	1m 32s
chunks (7, Client Integration Test)	5m 21s
chunks (8, TSO Integration Test)	1m 31s
chunks (8, TSO Integration Test)	4m 59s
chunks (9, MicroService Integration(!TSO))	1m 32s
chunks (9, MicroService Integration(!TSO))	5m 9s
chunks (10, MicroService Integration(TSO))	1m 32s
chunks (10, MicroService Integration(TSO))	5m 36s
report-coverage	1s
report-coverage	11s
	1h 8m 10s

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