Fix examples/VPC_EC2_Instance_With_Multiple_Dynamic_IPAddresses.py

It was broken since its introduction in fc88fd01c1b609c43b5fdd7faf90df99ab140634
- introduces ec2.NetworkInterfaceProperty
 - adds properties to NetworkInterface:
  - SecondaryPrivateIpAddressCount
  - NetworkInterfaceId
  - DeviceIndex
 - makes SubnetId not required