android webview can't get vertx session

android webview can't get session when using target="_blank" with link.

### Version 3.5.1 (maybe 3.5.0 included,not sure)

* vert.x core:

* vert.x web:

### Context

I used android webview to call a vertx url,when I switched from one page to another, the vertx server would always generate a new session id, so I lost session data set by previous page.

But,when I use iphone webview or PC Chrome to call the same vertx server, the session can be remembered correctly.  so the error is only subject to android webview 

### Do you have a reproducer?

we can reproducer the error following the steps below.

### Steps to reproduce

1. write a smiple verticle

public class Test1Verticle  extends AbstractVerticle {
	 Router router1 ; 
	  @Override
	  public void start() throws Exception {
	    router1 = Router.router(vertx);	 	    
	    router1.route().handler(CookieHandler.create());
	    router1.route().handler(SessionHandler.create(LocalSessionStore.create(vertx)));
	    router1.route("/h5/*").handler(StaticHandler.create("web/h5"));
	    router1.route("/hit").handler(this::hit);	
	    vertx.createHttpServer().requestHandler(router1::accept).listen(8080) ;    
	  }	  
	  private void hit(RoutingContext routingContext) {
		  Session session = routingContext.session();
	      Integer cnt = session.get("hitcount");
	      cnt = (cnt == null ? 0 : cnt) + 1;
	      session.put("hitcount", cnt);
		  routingContext.response().putHeader("content-type", "application/json;charset=UTF-8")
         .end(new JsonObject().put("data", "cnt="+cnt) );
	   } 
	  
	}

2.  place 2 html files in the web/h5 file folder,named test3.html and test4.html respectively. test3.html source code:

call test4

$.ajax({ url:"/hit?time="+(new Date().getTime()),  type:"post",  dataType : "json", success: function(resp){ console.log(resp) $("#myData").html(resp.data); }, error: function(){ $j("#myData").html("error."); me.resetload(); } });

the source code of test4.html is similar to the above,just replace the href to test3.html

3. ...

start the vertx verticle, and open an android browser,input the url (http://192.168.0.13:8080/h5/test3.html) in the browser,then submit

4.  you can find ,after jump to the other html,the hit count remains to 1, but if you call the url in iphone or PC browser, the hit count will be found to increment correctly.

5,if we remove the target="_blank" in the html file, the session will work properly

2018-04-21 13:42 update:

I tested on several android phone ,and foud that the session problem did not appear on all android phone, Mi and Huawei could reproduce this error,but sumsung and Lenovo worked correctly.

at last,I added some code in my verticle file to address this problem:

//to make session work correctly on Huawei phone, set Cookie Path to root '/' 
        Set ccList=routingContext.cookies();
        for(Cookie ck:ccList){
        	ck.setPath("/");        	
        }