Support for required EvaluateTargetHealth for ALIAS records

Note an error was being raised when using the old API about EvaluateTargetHealth being missing.

```
Excon::Errors::BadRequest: Expected(200) <=> Actual(400 Bad Request)
  response => #<Excon::Response:0x007fde3baf66a0 @data={:body=>"<?xml version=\"1.0\"?>\n<ErrorResponse xmlns=\"https://route53.amazonaws.com/doc/2013-04-01/\"><Error><Type>Sender</Type><Code>InvalidInput</Code><Message>Invalid XML ; cvc-complex-type.2.4.b: The content of element 'AliasTarget' is not complete. One of '{&quot;https://route53.amazonaws.com/doc/2013-04-01/&quot;:EvaluateTargetHealth}' is expected.</Message></Error><RequestId>f141b55c-f726-11e3-b2ac-73337c63db62</RequestId></ErrorResponse>", :headers=>{"x-amzn-RequestId"=>"f141b55c-f726-11e3-b2ac-73337c63db62", "Content-Type"=>"text/xml", "Content-Length"=>"438", "Date"=>"Wed, 18 Jun 2014 20:27:17 GMT"}, :status=>400, :remote_ip=>"72.21.214.31", :local_port=>60240, :local_address=>"192.168.1.85"}, @body="<?xml version=\"1.0\"?>\n<ErrorResponse xmlns=\"https://route53.amazonaws.com/doc/2013-04-01/\"><Error><Type>Sender</Type><Code>InvalidInput</Code><Message>Invalid XML ; cvc-complex-type.2.4.b: The content of element 'AliasTarget' is not complete. One of '{&quot;https://route53.amazonaws.com/doc/2013-04-01/&quot;:EvaluateTargetHealth}' is expected.</Message></Error><RequestId>f141b55c-f726-11e3-b2ac-73337c63db62</RequestId></ErrorResponse>", @headers={"x-amzn-RequestId"=>"f141b55c-f726-11e3-b2ac-73337c63db62", "Content-Type"=>"text/xml", "Content-Length"=>"438", "Date"=>"Wed, 18 Jun 2014 20:27:17 GMT"}, @status=400, @remote_ip="72.21.214.31", @local_port=60240, @local_address="192.168.1.85">
	from /gems/ruby-2.0.0-p353/gems/excon-0.37.0/lib/excon/middlewares/expects.rb:6:in `response_call'
	from /gems/ruby-2.0.0-p353/gems/excon-0.37.0/lib/excon/middlewares/response_parser.rb:26:in `response_call'
	from /gems/ruby-2.0.0-p353/gems/excon-0.37.0/lib/excon/connection.rb:402:in `response'
	from /gems/ruby-2.0.0-p353/gems/excon-0.37.0/lib/excon/connection.rb:272:in `request'
	from /gems/ruby-2.0.0-p353/gems/fog-1.22.1/lib/fog/xml/sax_parser_connection.rb:35:in `request'
	from /gems/ruby-2.0.0-p353/gems/fog-1.22.1/lib/fog/xml.rb:21:in `request'
	from /gems/ruby-2.0.0-p353/gems/fog-1.22.1/lib/fog/aws/dns.rb:126:in `request'
	from /gems/ruby-2.0.0-p353/gems/fog-1.22.1/lib/fog/aws/requests/dns/change_resource_record_sets.rb:120:in `change_resource_record_sets'
```
Merge pull request #3005 from ably-forks/evaluate_target_health-support

Support for required EvaluateTargetHealth for ALIAS records