etcdserver: apply config change on cluster store

goal:
make changes on cluster store according to config change

non-goal:
check on adding exsiting node / removing non-existant node

for #1016 
can we move line 435-438 into clusterStore.Create? or at least, we need to pass cc.NodeID into clusterStore.Create. 

we need to check if m.ID equals cc.NodeID.