ovsdb: raft: Support pre-vote mechanism to deal with disruptive server. #2283

Job	Run time
linux deb no dpdk	8m 16s
osx clang --disable-ssl	3m 53s
linux rpm fedora	6m 17s
dpdk gcc	7s
linux gcc --disable-ssl	3m 29s
linux clang --disable-ssl	3m 7s
linux gcc c99	3m 12s
linux clang c99	3m 3s
linux gcc test	10m 40s
linux clang test asan	19m 18s
linux clang test ubsan	15m 27s
linux gcc test --enable-shared	14m 56s
linux clang test --enable-shared	15m 37s
linux gcc test dpdk	14m 54s
linux clang test dpdk	14m 51s
linux gcc test -ljemalloc	10m 55s
linux clang test -ljemalloc	13m 50s
linux gcc --enable-afxdp	3m 20s
linux clang --enable-afxdp	3m 37s
linux gcc dpdk --enable-shared	5m 31s
linux clang dpdk --enable-shared	6m 6s
linux gcc dpdk-shared	3m 47s
linux clang dpdk-shared	4m 20s
linux gcc dpdk-shared --enable-shared	4m 57s
linux clang dpdk-shared --enable-shared	4m 11s
linux gcc m32 --disable-ssl	3m 23s
	3h 21m 4s

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