AWS::ElasticLoadBalancingV2::LoadBalancer can not use AWSHelperFn for Subnets and SecurityGroups

[kteague]

The 2020-06-11 change to Troposphere changed props for AWS::ElasticLoadBalancingV2::LoadBalancer SecurityGroups and Subnets from:

'Subnets': (list, False), -- to --> 'Subnets': ([basestring], False),

4d404fa

If you create a troposphere.elasticloadbalancingv2.LoadBalancer using from_dict the _from_dict validation is now triggered to check for a List. However, if you are using a AwsHelperFn such as a Troposphere.Ref for List<AWS::EC2::Subnet::Id> and List<AWS::EC2::SecurityGroup::Id> then validation will incorrectly fail.

Changing BaseAWSObject._from_dict from:

if isinstance(prop_type, list):

To

if isinstance(prop_type, list) and not isinstance(value, AWSHelperFn):

Fixes the problem by skipping validation on AWSHelperFn's. Basically bringing the validation in-sync with the behaviour of the BaseAWSObject.__setattr__ method.

Not sure if there are other considerations that change might have though ...