Returning 500 status code if NS cannot be contacted

CHANGELOG.md

@@ -7,7 +7,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 ## [4.0.0] - Unreleased
 ### Added
  - Multi query endpoint.  You no longer need to run a single instance per NetScaler you want to monitor.  The exporter now supports Prometheus targets so only one instance is required.
- - Up gauge.  This will be either 1 or 0 depending on whether the NetScaler responds or not.
+ - Return a 500 status code, and error message, if the NetScaler target cannot be contacted.
 
 ### Changed
  - Refactored exporter code into separate package for maintainability reasons.