Replace uses of AttributeKey.newInstance

The java driver uses netty channel attributes to decorate a
connection's channel with the cluster name (returned from
the system.local table) and the map from the OPTIONS response, both
of which are obtained on connection initialization.

There's an issue here that I wouldn't expect to see in practice in
that the AttributeKey's used are created using
AttributeKey.newInstance, which throws an exception if an
AttributeKey of that name is defined anywhere else in evaluated code.

This change attempts to resolve this issue by changing AttributeKey
initialiation in DriverChannel from newInstance to valueOf, which avoids
throwing an exception if an AttributeKey of the same name was previously
instantiated.

patch by Andy Tolbert; reviewed by Bret McGuire, Alexandre Dutra, Abe Ratnofsky for CASSANDRA-19290

Author: tolbertam

core/src/main/java/com/datastax/oss/driver/internal/core/channel/DriverChannel.java

@@ -49,9 +49,9 @@
 @ThreadSafe
 public class DriverChannel {
 
-  static final AttributeKey<String> CLUSTER_NAME_KEY = AttributeKey.newInstance("cluster_name");
+  static final AttributeKey<String> CLUSTER_NAME_KEY = AttributeKey.valueOf("cluster_name");
   static final AttributeKey<Map<String, List<String>>> OPTIONS_KEY =
-      AttributeKey.newInstance("options");
+      AttributeKey.valueOf("options");
 
   @SuppressWarnings("RedundantStringConstructorCall")
   static final Object GRACEFUL_CLOSE_MESSAGE = new String("GRACEFUL_CLOSE_MESSAGE");