Move error handling logic to the connection layer

It was previously spread between `RoutingSession`, `RoutingTransaction` and
`RoutingStatementResult` and they all did the same thing when connection
errors happened.

This commit introduces `RoutingPooledConnection` that handles errors for
routing driver by removing entries from the routing table and purging
connection pool for failed address.

Author: lutovich

driver/src/main/java/org/neo4j/driver/internal/ExplicitTransaction.java

@@ -39,7 +39,7 @@
 import static org.neo4j.driver.v1.Values.ofValue;
 import static org.neo4j.driver.v1.Values.value;
 
-class ExplicitTransaction implements Transaction
+public class ExplicitTransaction implements Transaction
 {
     private enum State
     {
@@ -71,7 +71,7 @@ private enum State
     private String bookmark = null;
     private State state = State.ACTIVE;
 
-    ExplicitTransaction( Connection conn, Runnable cleanup )
+    public ExplicitTransaction( Connection conn, Runnable cleanup )
     {
         this( conn, cleanup, null );
     }

driver/src/main/java/org/neo4j/driver/internal/NetworkSession.java

@@ -41,7 +41,7 @@
 
 public class NetworkSession implements Session
 {
-    protected Connection connection;
+    private final Connection connection;
     private final String sessionId;
     private final Logger logger;
 
@@ -67,7 +67,7 @@ public void run()
     private ExplicitTransaction currentTransaction;
     private AtomicBoolean isOpen = new AtomicBoolean( true );
 
-    NetworkSession( Connection connection )
+    public NetworkSession( Connection connection )
     {
         this.connection = connection;
 

driver/src/main/java/org/neo4j/driver/internal/RoutingDriver.java

@@ -63,8 +63,7 @@ public RoutingDriver(
     protected Session newSessionWithMode( AccessMode mode )
     {
         Connection connection = acquireConnection( mode );
-        Session networkSession = sessionFactory.newInstance( connection );
-        return new RoutingNetworkSession( networkSession, mode, connection.boltServerAddress(), loadBalancer );
+        return sessionFactory.newInstance( connection );
     }
 
     private Connection acquireConnection( AccessMode role )