This commit adds support for Raft cluster reconfiguration, takes care to
extract cluster config changes from the config block and apply those
changes to the replic set.

Change-Id: I564fafa418757e565ec2c0d872174d5d4f1ad719
Signed-off-by: Artem Barger <bartem@il.ibm.com>
Signed-off-by: Jay Guo <guojiannan1101@gmail.com>