When a shard becomes search active then trigger a refresh instead of waiting for the next scheduled refresh.
The `IndexShard#awaitShardSearchActive(...)` method registers a refresh listener and then often waits for the refresh scheduler to trigger a refresh. By default this is one second. In order to avoid increasing the query time of the Search API, the mentioned method should trigger a refresh instead for waiting it to happen.

As part of this change we also need to disable the refresh scheduler completely. Otherwise we run at risk of running two refreshes next after each other. One triggered from making shard search active and one from the refresh scheduler.  



server/src/main/java/org/elasticsearch/index/shard/IndexShard.java
* since we use Engine#writeIndexingBuffer for this now.
         */
        verifyNotClosed();
        final long time = System.nanoTime();
        
        PlainActionFuture<Engine.FlushResult> future = PlainActionFuture.newFuture();
        getEngine().flush(force, waitIfOngoing, future);
        Engine.FlushResult flushResult = future.actionGet();
        flushMetric.inc(System.nanoTime() - time);
        return flushResult.flushPerformed();
    }
    /**
     * checks and removes translog files that no longer need to be retained. See
     * {@link org.elasticsearch.index.translog.TranslogDeletionPolicy} for details
     */
    public void trimTranslog() {
        verifyNotClosed();
        final Engine engine = getEngine();
        engine.trimUnreferencedTranslogFiles();
    }
    /**
     * Rolls the tranlog generation and cleans unneeded.
     */
    public void rollTranslogGeneration() {
        final Engine engine = getEngine();
        engine.rollTranslogGeneration();
    }
    public void forceMerge(ForceMergeRequest forceMerge) throws IOException {
        IndexShardState state = this.state; 
        if (state != IndexShardState.STARTED) {