RATIS-2303. Migrate ratis-examples tests to Junit 5. #47

Job	Run time
CI / build / build	1m 18s
CI / release / release	5m 18s
CI / unit (grpc) / unit (grpc)	21m 7s
CI / unit (server) / unit (server)	18m 49s
CI / unit (misc) / unit (misc)	14m 51s
CI / unit (flaky) / unit (flaky)	5m 32s
CI / basic (rat) / rat	23s
CI / basic (checkstyle) / checkstyle	21s
CI / basic (findbugs) / findbugs	1m 52s
CI / basic (author) / author	8s
CI / compile (17) / compile (17)	59s
CI / compile (21) / compile (21)	1m 3s
CI / repro / repro	1m 15s
CI / compile (11) / compile (11)	57s
CI / coverage	35s
	1h 14m 28s

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