This CR enables optimistic creation of a chain of blocks in etcd/raft to
pipeline block creation and consensus on the created blocks. We cannot
do the pipelining for config blocks since all messages need to be
revalidated upon a config change.

Change-Id: Iabf1d4c75584afe8f641a18153d5e1b4b94f6bcc
Signed-off-by: Adarsh Saraf <adarshsaraf123@gmail.com>