Fix context switching between wd context methods

For example context depended searching like 

     ... .elementByClassName("soria")
            .elementByClassName("mid")
            .end(1)
            .elementByClassName("left")
            .elementByXPath("./..")
            .getAttribute("id").then(function(id) {
		assert.equal(id, "portal-header");
	     });

in DOM structure:

<body class="soria">
   <div id="portal-site-container">
      <div id="portal-header">
         <div class="mid">xxxx</div>
         <div class="left">yyyy</div>
       </div>
   </div>
</body>