Clarify ELB Health Check Port In Load Balancer Extension

Currently there is undocumented behavior in the AWS load balancer extension concerning which port AWS conducts the health check against.

We should clarify for the user that the first port added in the ELB port list is mapped to the ELB tcp check in AWS. If there are services which come up in a specific order and are dependent on each other, it is important to know which order to add ports in.