New option for route53: retry_interval

##### Issue Type

Feature Pull Request

##### Ansible Version:

ansible 1.6.6

But affects devel branch as well

##### Environment:

OSX 10.9.2

##### Summary:

The route53 module has a default, hard-coded, retry interval of 500 seconds (8 min 20sec).

If either Route53 is having a bad day, or you have many domains to manage, you're almost guaranteed to experience one or more 8+min retry intervals, which can really add up and make ansible take forever to run.

##### Steps To Reproduce:

Use the route53 module with more than a dozen or so domains and you're more than likely to experience one or more 8+ minute retry interval. 

I'm currently booting up a cluster of 15 machines, each with 2 Route53 records, and runtime is usually 20+ minutes just for the route53 part.

##### Expected Results:

I'd like to be able to customize the retry interval when managing many domains. For this patch, 15 seconds worked quite nicely.

##### Actual Results:

A very long wait. My beard got longer. I should have gone and made a snack or called my mom.