Add 'route53_replace_names' feature to ec2 dynamic inventory script

This commit adds a 'route53_replace_names' boolean to the inventory script. It aims at replacing the main name of EC2 instances by their first CNAME in Route 53 if any.

As of the implementation, I simply had to move the route53 related stuff up in the `add_instance` method and use the already collected route53 record sets. I think it's fair to avoid wildcard entries, tell me if I'm wrong.

The corresponding ML thread is here: https://groups.google.com/forum/#!topic/ansible-devel/NbidWZo1GgE

As mentionned in the ML, this change is an other option for / completes the following PRs: #7395, #7601, #9825