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.Common/Extensions/Base64Extensions.cs

@@ -0,0 +1,17 @@
+using System;
+
+namespace NzbDrone.Common.Extensions
+{
+    public static class Base64Extensions
+    {
+        public static string ToBase64(this byte[] bytes)
+        {
+            return Convert.ToBase64String(bytes);
+        }
+
+        public static string ToBase64(this long input)
+        {
+            return BitConverter.GetBytes(input).ToBase64();
+        }
+    }
+}