scylla-jmx: Fix tablemetricsobjectname breakage

Fixes #57

The usage of TableMetricsObjectName-yada-yada relies on translating the
"fake" objectname to a canonical one on remote
publication/serialization. However, the implementation of
ObjectName.getInstance has changed in JDK (micro) updates so it no
longer applies overridable methods -> wrong name published.

Fix by doing explicit ObjectName instansiation.
Message-Id: <20181023132005.23099-1-calle@scylladb.com>

src/main/java/com/scylladb/jmx/utils/APIMBeanServer.java

@@ -53,7 +53,16 @@ public class APIMBeanServer implements MBeanServer {
     }
 
     private static ObjectName prepareForRemote(final ObjectName n) {
-        return ObjectName.getInstance(n);
+        /*
+         * ObjectName.getInstance has changed in JDK (micro) updates so it no longer applies 
+         * overridable methods -> wrong name published. 
+         * Fix by doing explicit ObjectName instansiation. 
+         */
+        try {
+            return new ObjectName(n.getCanonicalName());
+        } catch (MalformedObjectNameException e) {
+            throw new IllegalArgumentException(n.toString());
+        }
     }
 
     @Override

src/main/java/org/apache/cassandra/metrics/TableMetrics.java

@@ -297,17 +297,16 @@ public class TableMetrics implements Metrics {
 
     @SuppressWarnings("serial")
     static class TableMetricObjectName extends javax.management.ObjectName {
-        private static final String FAKE_NAME = "a:a=a";
-
         private final TableMetricStringNameFactory factory;
         private final String metricName;
 
         public TableMetricObjectName(TableMetricStringNameFactory factory, String metricName) throws MalformedObjectNameException {
-            super(FAKE_NAME);
+            super("");
             this.factory = factory;
             this.metricName = metricName;
         }
 
+        
         @Override
         public boolean isPropertyValuePattern(String property) {
             return false;
@@ -356,8 +355,7 @@ public class TableMetrics implements Metrics {
         @Override
         public boolean equals(Object o) {
             if (this == o) return true;
-            if (!(o instanceof TableMetricObjectName)) return false;
-            return getCanonicalName().equals(((TableMetricObjectName) o).getCanonicalName());
+            return getCanonicalName().equals(((ObjectName) o).getCanonicalName());
         }
 
         @Override
@@ -372,6 +370,36 @@ public class TableMetrics implements Metrics {
             }
             return getCanonicalName().equals(name.getCanonicalName());
         }
+
+
+        @Override
+        public boolean isPattern() {
+            return false;
+        }
+
+
+        @Override
+        public boolean isDomainPattern() {
+            return false;
+        }
+
+
+        @Override
+        public boolean isPropertyPattern() {
+            return false;
+        }
+
+
+        @Override
+        public boolean isPropertyListPattern() {
+            return false;
+        }
+
+
+        @Override
+        public boolean isPropertyValuePattern() {
+            return false;
+        }
     }
 
     static interface TableMetricStringNameFactory {