Compare DNS names case insensitively.

##### Issue Type: Bug Fix Pull Request

##### Ansible Version: ansible 1.5.5

##### Environment: OS X

##### Summary:  If I try to override the value of a DNS name that is in lowercase with one that is uppercase, the Ansible module things they are no the same DNS name.

##### Steps To Reproduce:  Create a dns name in route53 that has mixed case. Then try to change its value with 'overwrite' set to true.

##### Expected Results: DNS name gets updiated with the new value.

##### Actual Results:

18:12:42 msg: Tried to create resource record set [name='******', type='CNAME'] but it already exists