title: RxJava2 .startWith(..) doesn't work
body: <p>I have <code>Observable</code> what emit some <code>String</code>:</p>
  
  <pre><code>List&lt;String&gt; list = // size this list is 5
  Observable o1 = Observable.fromArray(list.toArray());
  </code></pre>
  
  <p>and another one what emit one object per 10 second:</p>
  
  <pre><code>Observable intervalObservable = Observable.interval(10, TimeUnit.SECONDS);
  </code></pre>
  
  <p>I want to create Observable what every 10 second will emit every item from <code>o1</code>, so I did:</p>
  
  <pre><code>Observable change2tervalToString = intervalObservable.map(new Function() {
          @Override
          public Object apply(Object o) throws Exception {
              return "STARTER!";
          }
      });
  
  Observable per10sec = o1.startWith(change2tervalToString);
  </code></pre>
  
  <p>If I <code>.subscribe()</code> to <code>per10sec</code> it doesn't emit something like: </p>
  
  <pre><code>"STARTER", "ITEM_FROM_LIST1", "ITEM_FROM_LIST2", "ITEM_FROM_LIST3"...
  </code></pre>
  
  <p>but only (every 10 second):</p>
  
  <pre><code>"STARTER"
  </code></pre>
  
  <p>I want to achive something like this:</p>
  
  <pre><code>"STARTER", "ITEM_FROM_LIST1", "ITEM_FROM_LIST2", "ITEM_FROM_LIST3"...
  ....
  ....
   10 sec
  ....
  ....
  "STARTER", "ITEM_FROM_LIST1", "ITEM_FROM_LIST2", "ITEM_FROM_LIST3"...
  ....
  ....
  ....
  </code></pre>