Improve indexer health check messages (#1015)

* Improve indexer health check messages

Fixed: Improve health check message when all enabled indexers are disabled due to failures
Closes #1551

* Fixed: Health check failing and preventing others from running

* Fixed Indexer Health Checks and tests.

src/NzbDrone.Core/Indexers/XElementExtensions.cs

@@ -12,7 +12,7 @@ namespace NzbDrone.Core.Indexers
 {
     public static class XElementExtensions
     {
-        private static readonly Logger Logger = NzbDroneLogger.GetLogger(typeof(XmlExtentions));
+        private static readonly Logger Logger = NzbDroneLogger.GetLogger(typeof(XmlExtensions));
 
         public static readonly Regex RemoveTimeZoneRegex = new Regex(@"\s[A-Z]{2,4}$", RegexOptions.Compiled);