etcdserver: check error return for store#internalCreate
etcdserver: check error return for store#internalCreate

Signed-off-by: Ted Yu <22f3e725b314afeca4d45e12683c560674029d21@gmail.com>

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