AWS::ElasticLoadBalancingV2::ListenerCertificate updates remove existing listener certificates

## 1. Title

AWS::ElasticLoadBalancingV2::ListenerCertificate

## 2. Scope of request

Fix AWS::ElasticLoadBalancingV2::ListenerCertificate updates mistakenly remove existing certificates from the listener.

## 3. Expected behavior

When adding certificates to the list, existing certificates should not be touched.

## 4. Helpful Links to speed up research and evaluation

Bug has been confirmed and described in detail by AWS in https://forums.aws.amazon.com/thread.jspa?threadID=288095

## 5. Category
EC2

Start with the issue’s AWS forum link and the reported AWS::ElasticLoadBalancingV2::ListenerCertificate behavior. Confirm how an update that adds certificates affects existing listener certificates; done means existing certificates remain untouched while new certificates are added. No repository files or tests are named in the issue.

Written by the indexing model from the issue text.