Show the health check result in HealthCheckFailedException

Provide the output of the check results when rendering
the HealthCheckFailedException object in logs.

Change-Id: I5b1ef87ed36c3c709b70006ec0ea52627c2b037d

src/main/java/com/googlesource/gerrit/plugins/healthcheck/HealthCheckFailedException.java

diff --git a/src/main/java/com/googlesource/gerrit/plugins/healthcheck/HealthCheckFailedException.java b/src/main/java/com/googlesource/gerrit/plugins/healthcheck/HealthCheckFailedException.java
index 4ebba95..2ea0c14 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/healthcheck/HealthCheckFailedException.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/healthcheck/HealthCheckFailedException.java
@@ -26,4 +26,9 @@
   Map<String, Object> getResult() {
     return result;
   }
+
+  @Override
+  public String toString() {
+    return "Health check failed: " + result;
+  }
 }