Added better region handling and enabled eu-central-1

Make use of improved connect_to_aws that throws an exception
if a region can't be connected to (e.g. eu-central-1 requires
boto 2.34 onwards)

Add eu-central-1 to the two modules that hardcode their regions
Add us-gov-west-1 to ec2_ami_search to match documentation!
This pull request makes use of the changes in ansible/ansible#9419

lib/ansible/modules/cloud/amazon/ec2_elb_lb.py

@@ -375,7 +375,7 @@ class ElbManager(object):
         try:
             return connect_to_aws(boto.ec2.elb, self.region,
                                   **self.aws_connect_params)
-        except boto.exception.NoAuthHandlerFound, e:
+        except (boto.exception.NoAuthHandlerFound, StandardError), e:
             self.module.fail_json(msg=str(e))
 
     def _delete_elb(self):