title: Start obserable chain from Single.onErrorResumeNext in Rxjava2
body: <p><code>loadSingle</code> return Single object, if it fails I want to call <code>getObservable(rsList)</code> which return Observable.
  I am trying with <code>onErrorResumeNext</code> but it needs Single object.
  How can I call <code>getObservable(rsList)</code> on failure of <code>loadSingle()</code> ?</p>
  <p>Thanks in advance!!</p>
  <pre><code>                    repo.loadSingle()
                              .subscribeOn(Schedulers.io())
                              
                              .onErrorResumeNext {
                                  repo.getObservable(rsList)
                              }
                              .flatMapObservable {
                                  if (it != null &amp;&amp; it.status == Status.SUCCESS) {
                                      upRsList(it.data)
                                  }
                                  repo.getObservable(rsList)
                              }
                            
                              ({ //observable success
                               }, {
                                 //observable error 
                              })
  </code></pre>
  <p>Api interface</p>
  <pre><code>interface HomeApi{
      fun getSingel():Single&lt;List&lt;String&gt;&gt;
      fun getObservable():Observable&lt;HomeResponse&gt;
  }
  </code></pre>