raft: removed unused func
raft: move poll close to campaign
raft: group configuration related funcs
raft: group getter funcs
raft: one line
raft: group step funcs
etcdserver: apply entries when it is not empty

Or it updates appliedi wrongly.
etcdserver: init state before run loop correctly
Merge pull request #1889 from xiang90/chord_raft

Chord raft
Merge pull request #1891 from yichengq/257

etcdserver: init state before run loop correctly
snap: error on empty snapshot
Merge pull request #1894 from xiang90/fix_snap

snap: error on empty snapshot
raft: set raft.Commit too when setting raftLog.committed