Fixed wrong cross zone balancing error log.

If updating the cross zone balancing in the aws elb resource fails, the
error log claimed that the health check configuration failed. Fixed.

builtin/providers/aws/resource_aws_elb.go

@@ -328,7 +328,7 @@ func resourceAwsElbUpdate(d *schema.ResourceData, meta interface{}) error {
 		}
 		_, err := elbconn.ModifyLoadBalancerAttributes(&attrs)
 		if err != nil {
-			return fmt.Errorf("Failure configuring health check: %s", err)
+			return fmt.Errorf("Failure configuring cross zone balancing: %s", err)
 		}
 		d.SetPartial("cross_zone_load_balancing")
 	}