etcdserver: set default Raft logger with zap.Logger
etcdserver: set default Raft logger with zap.Logger

Signed-off-by: Gyuho Lee <3454051ee3341eb69bdf6fca40899cdad4d86496@gmail.com>

cockroachdb/etcd,etcd-io/etcd,bdarnell/etcd,vimalk78/etcd,gyuho/etcd,dannysauer/etcd,joshix/etcd,vimalk78/etcd,rnaveiras/etcd,mkumatag/etcd,dannysauer/etcd,mqliang/etcd,etcd-io/etcd,mqliang/etcd,joshix/etcd,glevand/coreos--etcd,sinsharat/etcd,mqliang/etcd,xiang90/etcd,gyuho/etcd,glevand/coreos--etcd,etcd-io/etcd,rnaveiras/etcd,ajityagaty/etcd,coreos/etcd,li-ang/etcd,ajityagaty/etcd,sebrandon1/etcd,bdarnell/etcd,coreos/etcd,li-ang/etcd,mkumatag/etcd,mkumatag/etcd,xiang90/etcd,rnaveiras/etcd,sebrandon1/etcd,sinsharat/etcd,ajityagaty/etcd,cockroachdb/etcd