integration: use variadic parameters for *Partition

'member' type is not exported.
In network partition tests, we want do

InjectPartition(t, clus.Members[lead], clus.Members[lead+1])

Signed-off-by: Gyu-Ho Lee <gyuhox@gmail.com>

clientv3/integration/network_partition_test.go

@@ -72,7 +72,7 @@ func testNetworkPartitionBalancer(t *testing.T, op func(*clientv3.Client, contex
 
 	// add other endpoints for later endpoint switch
 	cli.SetEndpoints(clus.Members[0].GRPCAddr(), clus.Members[1].GRPCAddr(), clus.Members[2].GRPCAddr())
-	clus.Members[0].InjectPartition(t, clus.Members[1:])
+	clus.Members[0].InjectPartition(t, clus.Members[1:]...)
 
 	for i := 0; i < 2; i++ {
 		ctx, cancel := context.WithTimeout(context.Background(), time.Second)