Fix RDS AWS connection

Use the common AWS connection improvements so that security_token,
boto_profile etc. are taken into account

library/cloud/rds

@@ -353,13 +353,13 @@ def main():
     apply_immediately  = module.params.get('apply_immediately')
     new_instance_name  = module.params.get('new_instance_name')
 
-    ec2_url, aws_access_key, aws_secret_key, region = get_ec2_creds(module)
+    region, ec2_url, aws_connect_params = get_aws_connection_info(module)
     if not region:
         module.fail_json(msg = str("region not specified and unable to determine region from EC2_REGION."))
 
     # connect to the rds endpoint
     try:
-        conn = boto.rds.connect_to_region(region, aws_access_key_id=aws_access_key, aws_secret_access_key=aws_secret_key)
+        conn = connect_to_aws(boto.rds, region, **aws_connect_params)
     except boto.exception.BotoServerError, e:
         module.fail_json(msg = e.error_message)