RATIS-2236 Fixed bug where manual triggerSnapshot would never finish #3733

Job	Run time
CI / build / build	1m 24s
CI / unit (server) / unit (server)	14m 32s
CI / unit (misc) / unit (misc)	7m 1s
CI / unit (grpc) / unit (grpc)	10m 50s
CI / basic (author) / author	5s
CI / basic (checkstyle) / checkstyle	23s
CI / basic (findbugs) / findbugs	1m 53s
CI / basic (rat) / rat	18s
CI / repro / repro	1m 26s
CI / compile (17) / compile (17)	1m 6s
CI / compile (21) / compile (21)	1m 9s
CI / compile (11) / compile (11)	59s
CI / coverage	0s
	41m 6s

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