CHANGELOG-3.4: add "code changes" from 3.3
CHANGELOG-3.4: add "code changes" from 3.3

Signed-off-by: Gyuho Lee <0fbd30d364d71722b926950b451cecd97b54fc29@amazon.com>

mqliang/etcd,cockroachdb/etcd,mqliang/etcd,mqliang/etcd,mkumatag/etcd,rnaveiras/etcd,li-ang/etcd,ajityagaty/etcd,etcd-io/etcd,etcd-io/etcd,dannysauer/etcd,rnaveiras/etcd,li-ang/etcd,mkumatag/etcd,ajityagaty/etcd,cockroachdb/etcd,mkumatag/etcd,coreos/etcd,etcd-io/etcd,coreos/etcd,dannysauer/etcd,ajityagaty/etcd,gyuho/etcd,rnaveiras/etcd,gyuho/etcd