Issue #4904 - WebsocketClient creates more connections than needed.

Fixed MultiplexConnectionPool.acquire() to use the new boolean
parameter to decide whether or not create a new connection.

This fixes ConnectionPoolTest instability.

Signed-off-by: Simone Bordet <simone.bordet@gmail.com>

jetty-client/src/main/java/org/eclipse/jetty/client/MultiplexConnectionPool.java

@@ -57,10 +57,10 @@ public class MultiplexConnectionPool extends AbstractConnectionPool implements C
     }
 
     @Override
-    public Connection acquire()
+    protected Connection acquire(boolean create)
     {
         Connection connection = activate();
-        if (connection == null)
+        if (connection == null && create)
         {
             int queuedRequests = getHttpDestination().getQueuedRequestCount();
             int maxMultiplex = getMaxMultiplex();