Test log consistency after apply_snapshot() is called.
Ensure log::last_term() log::last_conf_index() and log::size()
work as expected.
Misc cleanups.
* scylla-dev.git/raft-confchange-test-v4:
raft: fix spelling
raft: add a unit test for voting
raft: do not account for the same vote twice
raft: remove fsm::set_configuration()
raft: consistently use configuration from the log
raft: add ostream serialization for enum vote_result
raft: advance commit index right after leaving joint configuration
raft: add tracker test
raft: tidy up follower_progress API
raft: update raft::log::apply_snapshot() assert
raft: add a unit test for raft::log
raft: rename log::non_snapshoted_length() to log::in_memory_size()
raft: inline raft::log::truncate_tail()
raft: ignore AppendEntries RPC with a very old term
raft: remove log::start_idx()
raft: return a correct last term on an empty log
raft: do not use raft::log::start_idx() outside raft::log()
raft: rename progress.hh to tracker.hh
raft: extend single_node_is_quiet test
3cb01f218f