NetworkInterfaceProperty object does not support attribute Ipv6AddressCount

[klingenm]

troposphere.ec2.Instance(
            'SomeHost',
            ImageId='ami-0000',
            InstanceType='t2.micro',
            NetworkInterfaces=[NetworkInterfaceProperty(
                DeviceIndex=0,
                SubnetId='subnet-000000',
                AssociatePublicIpAddress=True,
                GroupSet=self.config.DefaultSecurityGroups,
                Ipv6AddressCount=1,
                Ipv6Addresses=[]
            )])

yields

AttributeError: NetworkInterfaceProperty object does not support attribute Ipv6AddressCount
and
AttributeError: NetworkInterfaceProperty object does not support attribute Ipv6Addresses (removing the Ipv6AddressCount argument naturally)

As a list item in troposphere.ec2.Instance argument NetworkInterfaces, NetworkInterfaceProperty should have member Ipv6AddressCount and Ipv6Addresses as documented on
http://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-properties-ec2-network-iface-embedded.html#aws-properties-ec2-network-iface-embedded-ipv6addresscount.

[markpeek]

Closed via #670.