synchronized int next() throws InterruptedException {
            if (freePorts.isEmpty()) {
                wait(600_000);
                if (freePorts.isEmpty()) {
                    throw new RuntimeException("no more ports in range " + first + "-" + last);
                }
            }
            int port = freePorts.pop();
            takenPorts.add(port);
            return port;
        }
Allocates port ranges for all configserver tests.

@author Ulf Lilleengen
configserver/src/test/java/com/yahoo/vespa/config/server/PortRangeAllocator.java