RATIS-2353. Refactor ReadOnlyRequestTests. (#1308) #300

Job	Run time
CI / build / build	1m 15s
CI / release / release	5m 36s
CI / basic (rat) / rat	28s
CI / basic (author) / author	9s
CI / basic (findbugs) / findbugs	1m 59s
CI / unit (grpc) / unit (grpc)	16m 23s
CI / basic (checkstyle) / checkstyle	30s
CI / unit (server) / unit (server)	17m 27s
CI / unit (misc) / unit (misc)	12m 30s
CI / unit (flaky) / unit (flaky)	5m 6s
CI / repro / repro	1m 14s
CI / compile (11) / compile (11)	1m 3s
CI / compile (21) / compile (21)	1m 8s
CI / compile (17) / compile (17)	1m 10s
CI / coverage	-1s
	1h 5m 57s

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