AMBARI-26596: Fixing fd leak during kerberizing

[HalimKim]

What changes were proposed in this pull request?

Using try-with-resources instead of just try in AbstractKerberosDescriptorFactory.java and AmbariMetaInfo.java

AbstractKerberosDescriptorFactory.java:

-      try {
-        return new Gson().fromJson(new FileReader(file),
+      try (FileReader reader = new FileReader(file)) {
+        return new Gson().fromJson(reader,
             new TypeToken<Map<String, Object>>() {
             }.getType());

AmbariMetaInfo.java:

-      try {
-        map = gson.fromJson(new FileReader(svc.getMetricsFile()), type);
+      try (FileReader reader = new FileReader(svc.getMetricsFile())) {
+        map = gson.fromJson(reader, type);

How was this patch tested?

manual tests done
I've built ambari-server jar file and updated my original ambari-server jar.
With the change, I've tried kerberizing test in my cluster.